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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Apr. 30, 2020	Jun. 24, 2020	Oct. 31, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Apr. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	KALV
Entity Registrant Name	KALVISTA PHARMACEUTICALS, INC.
Entity Central Index Key	0001348911
Current Fiscal Year End Date	--04-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NASDAQ
Entity File Number	001-36830
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-0915291
Entity Address, Address Line One	55 Cambridge Parkway
Entity Address, Address Line Two	Suite 901 East
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	999-0075
Entity Common Stock, Shares Outstanding		17,847,224
Entity Public Float			$ 164,278,175
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Information required in responses to Part III of Form 10-K is hereby incorporated by reference to portions of the Registrant’s Proxy Statement for the Annual Meeting of Stockholders to be held in 2020. The Proxy Statement will be filed by the Registrant with the Securities and Exchange Commission no later than 120 days after the end of the Registrant’s fiscal year ended April 30, 2020.

Consolidated Balance Sheets - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Current assets:
Cash and cash equivalents	$ 15,789	$ 32,006
Marketable securities	51,925	68,805
Research and development tax credit receivable	16,527	11,315
Prepaid expenses and other current assets	4,455	3,420
Total current assets	88,696	115,546
Property and equipment, net	2,043	2,413
Right of use assets	1,612
Other assets	178	173
Total assets	92,529	118,132
Current liabilities:
Accounts payable	1,677	2,860
Accrued expenses	5,455	5,647
Deferred revenue - current portion		9,545
Lease liability - current portion	588
Total current liabilities	7,720	18,052
Long-term liabilities:
Deferred revenue - net of current portion		3,342
Lease liability - net of current portion	1,057
Total long-term liabilities	1,057	3,342
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock, $0.001 par value, 100,000,000 authorized Shares issued and outstanding: 17,845,599 at April 30, 2020 and 17,277,750 at April 30, 2019	18	17
Additional paid-in capital	207,208	191,123
Accumulated deficit	(121,592)	(92,476)
Accumulated other comprehensive loss	(1,882)	(1,926)
Total stockholders’ equity	83,752	96,738
Total liabilities and stockholders’ equity	$ 92,529	$ 118,132

Consolidated Balance Sheets (Parenthetical) - $ / shares	Apr. 30, 2020	Apr. 30, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	17,845,599	17,277,750
Common stock, shares outstanding	17,845,599	17,277,750

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Income Statement [Abstract]
Revenue	$ 12,690	$ 16,127	$ 8,394
Operating expenses:
Research and development	40,194	35,021	18,237
General and administrative	13,029	10,926	8,862
Total operating expenses	53,223	45,947	27,099
Operating loss	(40,533)	(29,820)	(18,705)
Other income:
Interest income	1,830	1,397	82
Foreign currency exchange gain (loss)	(367)	49	(1,574)
Other income	9,830	7,682	4,392
Total other income	11,293	9,128	2,900
Loss before income taxes	(29,240)	(20,692)	(15,805)
Income tax (benefit) expense	(124)	124
Net loss	(29,116)	(20,816)	(15,805)
Other comprehensive income (loss):
Foreign currency translation adjustments	59	(1,257)	1,534
Unrealized holding gains on available-for-sale securities	285	440
Reclassification adjustment for realized (gain) on available for sale securities included in net loss	(300)
Comprehensive loss	$ (29,072)	$ (21,633)	$ (14,271)
Net loss per share to common stockholders, basic and diluted	$ (1.64)	$ (1.38)	$ (1.53)
Weighted average common shares outstanding, basic and diluted	17,748,666	15,080,863	10,321,780

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Apr. 30, 2017	$ 31,327	$ 10	$ 89,815	$ (55,855)	$ (2,643)
Balance, shares at Apr. 30, 2017		9,713,042
Issuance of ordinary shares/ common stock, net of issuance costs	9,101	$ 1	9,100
Issuance of ordinary shares/ common stock, net of issuance costs, shares		1,070,589
Issuance of common stock from exercise of stock options	36		36
Issuance of common stock from exercise of stock options, shares		16,264
Stock-based compensation expense	1,060		1,060
Net loss	(15,805)			(15,805)
Foreign currency translation adjustments	1,534				1,534
Balance at Apr. 30, 2018	27,253	$ 11	100,011	(71,660)	(1,109)
Balance, shares at Apr. 30, 2018		10,799,895
Issuance of ordinary shares/ common stock, net of issuance costs	87,910	$ 6	87,904
Issuance of ordinary shares/ common stock, net of issuance costs, shares		6,382,320
Issuance of common stock from exercise of stock options	242		242
Issuance of common stock from exercise of stock options, shares		95,535
Stock-based compensation expense	2,966		2,966
Net loss	(20,816)			(20,816)
Foreign currency translation adjustments	(1,257)				(1,257)
Unrealized holding gains from available-for-sale securities, net of reclassification for realized gains	440				440
Unrealized holding gains on available-for-sale securities	440
Balance at Apr. 30, 2019	96,738	$ 17	191,123	(92,476)	(1,926)
Balance, shares at Apr. 30, 2019		17,277,750
Issuance of ordinary shares/ common stock, net of issuance costs	11,422	$ 1	11,421
Issuance of ordinary shares/ common stock, net of issuance costs, shares		527,221
Issuance of common stock from exercise of stock options	$ 216		216
Issuance of common stock from exercise of stock options, shares	37,494	40,628
Stock-based compensation expense	$ 4,448		4,448
Net loss	(29,116)			(29,116)
Foreign currency translation adjustments	59				59
Unrealized holding gains on available-for-sale securities	285				285
Reclassification adjustment for realized (gain) on available for sale securities included in net loss	(300)				(300)
Balance at Apr. 30, 2020	$ 83,752	$ 18	$ 207,208	$ (121,592)	$ (1,882)
Balance, shares at Apr. 30, 2020		17,845,599

Consolidated Statement of Changes in Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Apr. 30, 2020 USD ($)
Statement Of Stockholders Equity [Abstract]
Stock issuance costs	$ 123

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Cash flows from operating activities:
Net loss	$ (29,116)	$ (20,816)	$ (15,805)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	512	378	180
Stock-based compensation expense	4,448	2,966	1,060
Realized gain from sale of marketable securities	(300)	(23)
Non-cash operating lease expense	13
Amortization of premium on available for sale securities	193
Foreign currency exchange (gain) loss	74	(80)	(651)
Changes in operating assets and liabilities:
Research and development tax credit receivable	(5,781)	(4,883)	(4,256)
Grants and other receivables			319
Prepaid expenses and other current assets	(1,112)	(1,979)	(746)
Other assets	(5)		(123)
Accounts payable	(1,004)	1,534	217
Accrued expenses	(48)	2,665	1,132
Deferred revenue	(12,690)	(16,127)	29,231
Net cash (used in) provided by operating activities	(44,816)	(36,365)	10,558
Cash flows from investing activities:
Purchases of available for sale securities	(49,797)	(79,889)
Sales and maturities of available for sale securities	66,770	11,548
Acquisition of property and equipment	(220)	(1,081)	(1,427)
Net cash provided by (used in) investing activities	16,753	(69,422)	(1,427)
Cash flows from financing activities:
Issuance of common stock, net of offering expenses	11,422	87,910	9,137
Issuance of common stock from equity incentive plans	216	242
Finance lease principal payments	(54)	(209)	(151)
Net cash provided by financing activities	11,584	87,943	8,986
Effect of exchange rate changes on cash and cash equivalents	262	(1,205)	1,988
Net (decrease) increase in cash and cash equivalents	(16,217)	(19,049)	20,105
Cash and cash equivalents, beginning year	32,006	51,055	30,950
Cash and cash equivalents, end of year	15,789	$ 32,006	51,055
Supplemental disclosures of cash flow information:
Right of use assets obtained in exchange for operating lease liabilities	$ 309
Capital leases			513
Acquisition of property and equipment in accounts payable			$ 291

Description of Business and Basis of Presentation

12 Months Ended

Apr. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of Business and Basis of Presentation

Note 1. Description of Business and Basis of Presentation

KalVista Pharmaceuticals, Inc. (together with its subsidiaries, “KalVista” or the “Company”) is a clinical stage pharmaceutical company focused on the discovery, development and commercialization of small molecule protease inhibitors for diseases with significant unmet need. The Company’s first product candidates are inhibitors of plasma kallikrein being developed for two indications: hereditary angioedema (“HAE”) and diabetic macular edema (“DME”). The Company applies its insights into the chemistry of proteases and, with current programs, the biology of the plasma kallikrein system, to develop small molecule inhibitors with high selectivity, potency and bioavailability that it believes will make them successful treatments for HAE and DME.

KalVista has created a structurally diverse portfolio of oral plasma kallikrein inhibitors and advanced multiple drug candidates into clinical trials in order to create best-in-class oral therapies for both HAE and DME. The Company is currently evaluating KVD900 in a Phase 2 clinical study as a potential on-demand therapy for acute HAE attacks, which is expected to complete in the second half of 2020. KVD824 is KalVista’s next oral program to be developed for HAE, and the Company plans to commence a Phase 2 clinical trial intended to evaluate KVD824 as a twice-daily potential oral prophylactic treatment for HAE in the second half of 2020. In the case of DME, the Company is initially developing a plasma kallikrein inhibitor which is administered directly into the eye and anticipates ultimate development of orally delivered drugs.

The KVD001 program, which was the lead DME candidate, as well as KalVista’s planned future oral DME programs were subject to an option agreement with Merck Sharpe & Dohme Corp. (“Merck”) entered into in 2017 (the “Option Agreement”). Under the terms of the Option Agreement, Merck had a defined period following receipt of a clinical data package including the results of the Phase 2 trial for KVD001, which were announced in December 2019, to determine whether to exercise its option to acquire KVD001 and to maintain its option on the oral DME programs. In February 2020, Merck notified the Company that those options would not be exercised. As a result, KalVista has retained all the rights and intellectual property that were subject to the Option Agreement, Merck has no further rights or obligations to the Company and the Company has no obligations to Merck.

The Company’s headquarters is located in Cambridge, Massachusetts, with research activities located in Porton Down, United Kingdom and Boston, Massachusetts.

The Company has devoted substantially all of its efforts to research and development, including clinical trials of its product candidates. The Company has not completed the development of any product candidates. Pharmaceutical drug product candidates, like those being developed by the Company, require approvals from the U.S. Food and Drug Administration (“FDA”) or foreign regulatory agencies prior to commercial sales. There can be no assurance that any product candidates will receive the necessary approvals and any failure to receive approval or delay in approval may have a material adverse impact on the Company’s business and financial results. The Company has not yet commenced commercial operations. The Company is subject to a number of risks and uncertainties similar to those of other life science companies developing new products, including, among others, the risks related to the necessity to obtain adequate additional financing, to successfully develop product candidates, to obtain regulatory approval of product candidates, to comply with government regulations, to successfully commercialize its potential products, to the protection of proprietary technology and to the dependence on key individuals.

The Company has funded its operations primarily through the issuance of stock and the Option Agreement. As of April 30, 2020, the Company had an accumulated deficit of $121.6 million and cash, cash equivalents and marketable securities totaling $67.7 million. The Company’s working capital, primarily cash and marketable securities, is anticipated to fund the Company’s operations for at least 12 months beyond the date of issuance of the consolidated financial statements.

The Company will need to expend substantial resources for research and development, including costs associated with the clinical testing of its product candidates and will need to obtain additional financing to fund its operations and to conduct trials for its product candidates. The Company will seek to finance future cash needs through equity offerings, future grants, corporate partnerships and product sales.

The Company has never been profitable and has incurred significant operating losses in each year since inception. Cash requirements may vary materially from those now planned because of changes in the Company’s focus and direction of its research and development programs, competitive and technical advances, patent developments, regulatory changes or other developments. Additional financing will be required to continue operations after the Company exhausts its current cash resources and to continue its long-term plans for clinical trials and new product development. There can be no assurance that any such financing can be obtained by the Company, or if obtained, what the terms thereof may be, or that any amount that the Company is able to raise will be adequate to support the Company’s working capital requirements until it achieves profitable operations. If adequate additional working capital is not secured when needed, the Company may be required to make reductions in spending, extend payment terms with suppliers, liquidate assets where possible and/or suspend or curtail planned research programs. Any of these actions could materially harm the Company’s business and prospects.

The outbreak of COVID-19 has evolved into a global pandemic. The extent of the impact of COVID-19 on the Company’s operational and financial performance will depend on certain developments, including the duration and spread of the outbreak, impact on clinical studies, employee or industry events, and effect on suppliers and manufacturers, or impact on the healthcare systems, all of which are uncertain and cannot be predicted. The Company has experienced and may continue to experience constrained supplies of product candidates or, with respect to the Company’s clinical trials, delays in enrollment, site initiation, participant dosing, distribution of clinical trial materials, study monitoring and data analysis that could materially adversely impact the Company’s business, results of operations and overall financial performance in future periods. Any such delays to the Company’s planned clinical timelines for KVD900 and KVD824 could also impact the use and sufficiency of existing cash reserves, and the Company may be required to raise additional capital earlier than previously planned. The Company may be unable to raise additional capital if and when needed, which may result in further delays or suspension of our development plans. The extent to which COVID-19 may impact the Company’s financial condition, results of operations or cash flows is uncertain. The impact of COVID-19 could have a material adverse impact on the Company’s operations and will continue to be monitored closely.

Summary of Significant Accounting Policies

12 Months Ended

Apr. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

Principles of consolidation: The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of estimates: The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates.

Foreign currency: The functional currency of the Company’s UK subsidiary is the British Pound Sterling. Assets and liabilities of the foreign subsidiary are translated using the exchange rate existing on each respective balance sheet date. Revenues and expenses are translated using average exchange rates prevailing throughout the year. The translation adjustments resulting from this process are included as a component of the accumulated other comprehensive loss. In addition, the Company engages in transactions and holds balances denominated and settled in currencies other than the functional currency, and transaction gains or losses are recorded in the consolidated statement of operations.

Segment Reporting: The chief operating decision maker, the CEO, manages the Company’s operations as a single operating segment for the purposes of assessing performance and making operating decisions.

Cash and cash equivalents: Cash and cash equivalents consist of bank deposits and money market accounts. Cash equivalents are carried at cost which approximates fair value due to their short-term nature. The Company considers all highly-liquid investments with an original maturity of 90 days or less to be cash equivalents.

The Company maintains its cash and cash equivalent balances with financial institutions that management believes are of high credit quality. The Company’s cash and cash equivalent accounts at times may exceed federally insured limits. The Company has not experienced any losses in such accounts. The Company believes it is not exposed to any significant credit risk of cash and cash equivalents.

Research and development tax credit receivable: The research and development tax credit receivable consists of research and development expenses that have been claimed as research and development tax credits in accordance with the relevant U.K. tax legislation. These refundable tax credits are payable to the Company in cash and are carried on the consolidated balance sheet at the amount claimed and expected to be received from the U.K. government within the next 12 months.

Property and equipment: Property and equipment are stated at cost less accumulated depreciation. Expenditures for repairs and maintenance are charged to expense as incurred. Upon retirement or sale, the costs of the assets disposed of and the related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the statement of operations. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which are as follows:

Asset Classification		Estimated Useful Life
Machinery and equipment		1-5 Years
Computer equipment		3-4 Years
Motor vehicles		4 Years
Leasehold improvements		5 Years or term of lease, if shorter

The Company assesses the impairment of long-lived assets whenever events or changes in circumstances indicate that the carrying value of such assets, or asset groups, may not be recoverable. Whenever events or changes in circumstances suggest that the carrying amount of long-lived assets may not be recoverable, the future undiscounted cash flows expected to be generated by the asset, or asset groups, from its use or eventual disposition is estimated. If the sum of the expected future undiscounted cash flows is less than the carrying amount of those assets, or asset groups, an impairment loss is recognized based on the excess of the carrying amount over the fair value of the assets, or asset groups.

Revenue recognition: The Company recognizes revenue from research and development arrangements. In accordance with Accounting Standards Codification (“ASC”) 606, “Revenue from Contracts with Customers,” revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these goods and services.

Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation.

The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes.

If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices.

The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either: (1) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, (2) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced or (3) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. ASC 606 requires the Company to select a single revenue recognition method for the performance obligation that faithfully depicts the Company’s performance in transferring control of the goods and services. The guidance allows for two methods to measure progress toward complete satisfaction of a performance obligation, depending on the facts and circumstances:

Output methods - recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g., surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units of produced or units delivered); and

Input methods - recognize revenue on the basis of the entity’s efforts or inputs to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs to the satisfaction of that performance obligation.

Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company must consider the nature of the intellectual property to which the customer will have rights (i.e., access at a point in time or benefit of intellectual property enhancements over time). The Company recognizes revenue from non-refundable, up-front fees allocated to the license at a point in time/over the period the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Milestone payments: At the inception of each arrangement that includes development and regulatory milestone payments for promised goods and services, the Company evaluates the circumstances of whether the milestones will be reached and estimates the amount to be included in the transaction price that will not cause a significant revenue reversal. Upon expiration of the Option Agreement, there are no outstanding milestones that can be reached.

Up-front payments: Up-front payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

Contract Balances: The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as a receivable (i.e., accounts receivable). A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities (i.e., deferred revenue) primarily relate to contracts where the Company has received payment but has not yet satisfied the related performance obligations. The advance consideration received from customers for research and development services and/or licenses is a contract liability, recorded as deferred revenue, until the underlying performance obligations are transferred to the customer.

Research and development: Research and development costs are expensed as incurred and include, but are not limited to:

•

Employee-related expenses including salaries, benefits, travel, and share-based compensation expense for research and development personnel;

•

Costs associated with preclinical and development activities;

•

Costs associated with regulatory operations.

Costs for certain research and development activities, such as manufacturing development activities and clinical studies are recognized based on the contracted amounts adjusted for the percentage of work completed to date. Payments for these activities are based on the terms of the contractual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued expenses. The Company defers and capitalizes non-refundable advance payments made by the Company for research and development activities until the related goods are delivered or the related services are performed.

Income taxes: The Company accounts for income taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The Company evaluates the realizability of its deferred tax assets and establishes a valuation allowance when it is more likely than not that all or a portion of deferred tax assets will not be realized. The Company has provided a full valuation allowance on its deferred tax assets.

Relative to accounting for uncertainties in tax positions, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, the Company does not recognize a tax benefit in the financial statements.

The Company recognizes interest and penalties related to uncertain tax positions, if any, as a component of income tax expense. As the Company has no uncertain tax positions, there were no interest or penalties charges recognized in the statement of operations for any years.

Stock-based compensation: The Company accounts for stock-based compensation arrangements at fair value. The fair value is recognized over the period during which the recipient is required to provide services (usually the vesting period), on a straight-line basis. Forfeitures are recognized as they are incurred.

Net Loss per Share: Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing net loss by the sum of the weighted average number of common shares and the number of potential dilutive common share equivalents outstanding during the period. Potential dilutive common share equivalents consist of the incremental common shares issuable upon the exercise of share options and awards.

Potential dilutive common share equivalents consist of:

	April 30,
	2020		2019		2018
Stock options and awards		2,320,677		1,784,338		388,366

In computing diluted earnings per share, common share equivalents are not considered in periods in which a net loss is reported, as the inclusion of the common share equivalents would be anti-dilutive. As a result, there is no difference between the Company’s basic and diluted loss per share in the periods presented.

Fair value measurement: The Company classifies fair value measurements using a three level hierarchy that prioritizes the inputs used to measure fair value. This hierarchy requires entities to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: Level 1, quoted market prices in active markets for identical assets or liabilities; Level 2, observable inputs other than quoted market prices included in Level 1, such as quoted market prices for markets that are not active or other inputs that are observable or can be corroborated by observable market data; and Level 3, unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities, including certain pricing models, discounted cash flow methodologies and similar techniques that use significant unobservable inputs. These fair values are obtained from independent pricing services, which utilize Level 1 and Level 2 inputs.

The following tables summarize the cash equivalents and marketable securities measured at fair value on a recurring basis as of April 30, 2020 and 2019:

	Level 1		Level 2		Level 3		Balance at April 30, 2020
Cash equivalents	$	650	$	—	$	—	$	650
Marketable securities:
Corporate debt securities		—		39,216		—		39,216
U.S. government agency securities		—		12,709		—		12,709
	$	650	$	51,925	$	—	$	52,575

	Level 1		Level 2		Level 3		Balance at April 30, 2019
Cash equivalents	$	30,044	$	1,962	$	—	$	32,006
Marketable securities:
Corporate debt securities		—		56,487		—		56,487
U.S. government agency securities		—		12,318		—		12,318
	$	30,044	$	70,767	$	—	$	100,811

Recently adopted accounting pronouncements: The Company adopted ASC 842, Leases (“ASC 842”), using the modified retrospective approach, effective May 1, 2019. The Company elected the package of practical expedients permitted under the transition guidance within the new standard which allows the Company to not reassess previous accounting conclusions around whether arrangements are or contain leases, the classification of its existing leases as of the transition date, and the treatment of initial direct costs. In addition, the Company elected the practical expedient not to apply the recognition requirements in the lease standard to short-term leases (a lease that at commencement date has a lease term of 12 months or less and does not contain a purchase option that the lessee is reasonably certain to exercise) and the practical expedient that permits lessees to make an accounting policy election (by class of underlying asset) to account for each separate lease component of a contract and its associated non-lease components as a single lease component.

As a result of the adoption of the new lease accounting standard, the Company recognized operating lease assets and operating lease liabilities of $1.9 million, respectively on May 1, 2019. The adoption of the standard had no impact to the Company’s consolidated statement of operations or cash flows.

Marketable Securities

12 Months Ended

Apr. 30, 2020

Investments Debt And Equity Securities [Abstract]

Marketable Securities

Note 3. Marketable Securities

The objectives of the Company’s investment policy are to ensure the safety and preservation of invested funds, as well as to maintain liquidity sufficient to meet cash flow requirements. The Company invests its excess cash in securities issued by financial institutions, commercial companies, and government agencies that management believes to be of high credit quality in order to limit the amount of its credit exposure. The Company has not realized any significant losses from its investments.

The Company classifies all of its investments as available for sale. Unrealized gains and losses on investments are recognized in accumulated comprehensive loss, unless an unrealized loss is considered to be other than temporary, in which case the unrealized loss is charged to operations. The Company periodically reviews its investments for other than temporary declines in fair value below cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The Company believes the individual unrealized losses represent temporary declines primarily resulting from interest rate changes. Realized gains and losses are included in other income in the consolidated statements of operations and comprehensive loss and are determined using the specific identification method with transactions recorded on a trade date basis.

The following tables summarize the fair value of the Company’s investments by type as of April 30, 2020 and 2019:

	April 30, 2020
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities	$	38,922	$	295	$	(1	)	$	39,216
Obligations of the U.S. Government and its agencies		12,534		175		—			12,709
Total investments	$	51,456	$	470	$	(1	)	$	51,925

	April 30, 2019
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities	$	56,083	$	405	$	(1	)	$	56,487
Obligations of the U.S. Government and its agencies		12,282		36		—			12,318
Total investments	$	68,365	$	441	$	(1	)	$	68,805

The following table summarizes the scheduled maturity for the Company’s investments at April 30, 2020:

	April 30,
	2020
Maturing in one year or less	$	32,391
Maturing after one year through two years		11,698
Maturing after two years		7,836
Total investments	$	51,925

Property and Equipment

12 Months Ended

Apr. 30, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

Note 4. Property and Equipment

At April 30, 2020 and 2019, property and equipment consisted of (in thousands):

	2020			2019
Laboratory equipment	$	1,543		$	1,391
Office equipment		36			36
Furniture & fixtures		185			175
Leasehold improvements		1,647			1,707
Total property and equipment at cost		3,411			3,309
Less: Accumulated depreciation		(1,368	)		(896	)
Property and equipment, net	$	2,043		$	2,413

For the years ended April 30, 2020, 2019 and 2018, depreciation expense was $512,000, $378,000 and $180,000, respectively.

Accrued Expenses

12 Months Ended

Apr. 30, 2020

Payables And Accruals [Abstract]

Accrued Expenses

Note 5. Accrued Expenses

At April 30, 2020 and 2019, accrued expenses consisted of (in thousands):

	2020		2019
Accrued research expense	$	2,821	$	3,065
Accrued compensation		2,333		1,949
Accrued professional fees		173		186
Other accrued expenses		128		447
Total accrued expenses	$	5,455	$	5,647

Merck Arrangement

12 Months Ended

Apr. 30, 2020

License And Collaboration Arrangements [Abstract]

Merck Arrangement

Note 6. Merck Arrangement

On October 6, 2017, the Company’s wholly-owned U.K. based subsidiary KalVista Pharmaceuticals Limited (“KalVista Limited”) and Merck entered into the Option Agreement. Under the terms of the Option Agreement, the Company, through KalVista Limited, granted to Merck an option to acquire KVD001 through a period following completion of a Phase 2 clinical trial. The Company, through KalVista Limited, also granted to Merck a similar option to acquire investigational orally delivered molecules for DME (the “Oral DME Compounds”) through a period following the completion of a Phase 2 clinical trial. The Company, through KalVista Limited, also granted to Merck a non-exclusive license to use the compounds solely for research purposes, and was required to use its diligent efforts to develop the two compounds through the completion of Phase 2 clinical trials. The Company’s development efforts under the Option Agreement were governed by a joint steering committee consisting of equal representatives from the Company and Merck.

Under the terms of the Option Agreement, Merck paid a non-refundable upfront fee of $37 million to KalVista Limited in November 2017.

The Company evaluated the revenue arrangement in accordance with the provisions of ASC 606 upon the adoption of this guidance on May 1, 2018. The Company determined that the revenue arrangement contained the following promised services: (i) a non-exclusive license to use the two compounds solely for research purposes, (ii) research and development services related to the development of KVD001 through completion of a Phase 2 clinical trial, and (iii) research and development services related to the development of the Oral DME Compounds.

The Company further determined that the research license granted is not distinct from the respective research and development services, as the license could not be used on its own by Merck for its intended purpose of developing and commercializing KVD001 and the Oral DME Compounds and is significantly interdependent with the respective research and development services. As a result, the research license was combined with the respective research and development services for KVD001 and the Oral DME Compounds as two performance obligations.

The amounts allocated to each performance obligation were recognized as revenue using an input method of performance completed to date comparing the total effort incurred with the Company’s estimate of total effort required to perform the R&D services for each respective performance obligation. For the fiscal years ended April 30, 2020, 2019 and 2018, the Company recognized approximately $12.7 million, $16.1 million, and $8.0 million of revenue with respect to the arrangement with Merck, all of which was recognized from the deferred revenue balance.

On February 10, 2020, the Company announced that the Option Agreement had expired. As a result of the expiration, KalVista has no further obligations to Merck. The Company has retained full ownership of all of its DME intellectual property in additional to its oral HAE portfolio. The Company concluded that the performance obligations were completed in the fourth quarter of the fiscal year ended April 30, 2020. As a result, the Company recognized the remaining $3.8 million of deferred revenue from the Option Agreement, after which no additional revenue remains.

Stock-Based Compensation

12 Months Ended

Apr. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 7. Stock-Based Compensation

The Company has three plans that provide for equity-based compensation. Two are legacy plans for which no further grants are to be made. As of April 30, 2020, 942,122 stock options remain available for grant under the 2017 Equity Incentive Plan (“2017 Plan”). There are 3,538,090 shares of the Company’s common stock that are reserved for issuance upon exercise or settlement of stock options or other awards under all plans.

Initial awards generally vest 25% after one year and then ratably on a monthly basis over the next three years. Recurring grants typically vest on a monthly basis over four years. Stock option grants expire after ten years.

The Company recognizes stock-based compensation expense over the requisite service period based on the grant date fair value of the award. The Company has elected to use the Black-Scholes option pricing model to determine the fair value of awards granted. The determination of the fair value of stock-based awards utilizing the Black-Scholes model is affected by the share price and a number of assumptions, including expected volatility, expected life, risk-free interest rate and expected dividends. Due to insufficient history of the Company’s stock price, the stock-price volatility assumption is based on the historical volatility of a peer group of publicly traded companies. The expected life of the awards is estimated based on the simplified method. The risk-free interest rate assumption is based on observed interest rates appropriate for the terms of the awards. The dividend yield assumption is based on history and expectation of paying no dividends. Forfeitures have not been material in the periods presented.

The fair value of the share-based awards was measured with the following weighted-average assumptions for the fiscal years ended April 30:

	2020	2019	2018
Risk-free interest rate	2.06	2.90	1.94
Expected life of the options	6.25 years	6.25 years	6.25 years
Expected volatility of the underlying stock	81.1%	77.2%	76.9%
Expected dividend rate	0%	0%	0%

Stock-based compensation was reflected in the Company’s consolidated statement of operations and comprehensive loss as follows (in thousands):

	Year ended April 30,
	2020		2019		2018
Research and development	$	1,944	$	2,005	$	320
General and administrative		2,504		961		740
Total stock-based compensation expense	$	4,448	$	2,966	$	1,060

A summary of option activity for the year ended April 30, 2020 and changes during the years then ended is presented below:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
Outstanding at May 1, 2019		1,739,338		$	9.95		8.47	$	22,807
Exercised		(37,494	)		4.39
Granted		586,500			22.90
Cancelled		(12,667	)		19.89
Outstanding at April 30, 2020		2,275,677		$	13.32		7.83	$	4,899
Exercisable at April 30, 2020		1,157,171		$	9.73		7.25	$	3,931
Vested and expected to vest at April 30, 2020		2,275,677		$	13.32		7.83	$	4,899

The weighted-average grant date fair value of stock options granted during the years ended April 30, 2020, 2019 and 2018 was $15.76, $9.62, and $4.87, respectively. The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the years ended April 30, 2020, 2019 and 2018 was $431,000, $950,000 and $131,000, respectively. The total cash received by the Company as a result of employee stock option exercises during the years ended April 30, 2020, 2019 and 2018 was $216,000, $242,000, and $36,000, respectively. The Company has 45,000 performance-based restricted stock unit awards outstanding as of April 30, 2020. The performance period for these awards ends June 30, 2022.

As of April 30, 2020, there was $10.2 million of unrecognized compensation expense related to unvested awards, which is expected to be recognized over a weighted-average period of 2.3 years.

Commitments and Contingencies

12 Months Ended

Apr. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 8. Commitments and Contingencies

Clinical Studies: The Company enters into contractual agreements with contract research organizations in connection with preclinical and toxicology studies and clinical trials. Amounts due under these agreements are invoiced to the Company on predetermined schedules during the course of the studies and clinical trials and are not refundable regardless of the outcome. The Company has a contractual obligation related to the expected future costs to be incurred to complete the ongoing preclinical studies and clinical trials. The remaining commitments, which have cancellation provisions, totaled $3.6 million at April 30, 2020.

Indemnification: In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves future claims that may be made against the Company but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. No amounts associated with such indemnifications have been recorded to date.

Contingencies: From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business activities. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. There were no contingent liabilities requiring accrual at April 30, 2020 and 2019.

As a result of the terms of grant income received in prior years, upon successful regulatory approval and following the first commercial sale of certain products, the Company will be required to pay royalty fees of up to $1 million within 90 days of the first commercial sale of the product subject to certain caps and follow on payments depending upon commercial success and type of product. Given the stage of development of the current pipeline of products it is not possible to predict with certainty the amount, if any or timing of any such liability.

Leases

12 Months Ended

Apr. 30, 2020

Leases [Abstract]

Leases

Note 9. Leases

The Company has a lease agreement for approximately 2,700 square feet of space for its headquarters located in Cambridge, Massachusetts that commenced in September 2017 for a term of five years.

In April 2018, the Company entered into a lease agreement for approximately 8,800 square feet of office and research laboratory space located in Porton Down, United Kingdom for a term of ten years. In February 2020, the Company entered into a lease agreement, pursuant to which the Company leases approximately 4,600 square feet of additional office and research laboratory space located at the Porton Down facility for a term of eight years. The Company has the right to terminate the lease agreements on or after April 30, 2023. It is not likely that the Company will terminate either lease at that time, therefore the entire lease terms are included in the calculation of the lease liabilities. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew.

The Company is also party to several operating leases for office and laboratory space as well as certain lab equipment. Total rent expense was $743,000, $677,000 and $638,000 for the years ended April 30, 2020, 2019 and 2018, respectively and is reflected in general and administrative expenses and research and development expenses as determined by the underlying activities.

Incremental borrowing rate – The Company’s lease agreements do not provide an implicit rate. The Company estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term and economic environment.

Lease and non-lease components – The Company has elected the practical expedient which allows non-lease components to be combined with lease components for all existing asset classes and will therefore include any fixed additional rent amounts in its lease payments. Any variable lease payments are excluded from the lease liability and are recognized in the period incurred.

The following table summarizes lease costs included in research and development and general and administrative expense for the year ended April 30, 2020 (in thousands):

	Year Ended
	April 30, 2020
Operating lease costs	$	743
Finance lease costs		54
Short-term lease costs		13
Variable lease costs		47
Total lease costs	$	857

The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of April 30, 2020 (in thousands):

Years ending April 30,	Operating Leases
2021	$	679
2022		383
2023		239
2024		142
2025		142
Thereafter		439
Total lease payments		2,024
Less: imputed interest	379
Total lease liabilities		1,645
Current lease liabilities	588
Long-term lease liabilities	$	1,057

Disclosures related to relevant periods prior to adoption of Topic 842:

Future minimum payments under these leases as of April 30, 2019 are as follows (in thousands):

Years ending April 30,	Finance Leases		Operating Leases
2020	$	54	$	687
2021		—		474
2022		—		328
2023		—		194
2024 and thereafter		—		495
Total minimum lease payments	$	54	$	2,178
Less amounts representing interest		—
Present Value of minimum payments		54
Current portion		54
Long-term portion	$	—

The following table summarizes the lease term and discount rate as of April 30, 2020:

	April 30, 2020
Weighted-average remaining lease term (years)
Operating leases	4.8
Weighted-average discount rate
Operating leases		9.0	%

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the year ended April 30, 2020 (in thousands):

	April 30, 2020
Cash paid for amounts included in the measurement of operating lease liabilities	$	708
Cash paid for amounts included in the measurement of finance lease liabilities	$	54

Income Taxes

12 Months Ended

Apr. 30, 2020

Income Tax Disclosure [Abstract]

Income Taxes

Note 10. Income Taxes

The components of the Company’s loss before income taxes for the years ended April 30, 2020, 2019 and 2018 consisted of the following (in thousands):

	2020			2019			2018
Domestic	$	(6,337	)	$	(5,006	)	$	(4,020	)
Foreign		(22,903	)		(15,686	)		(11,785	)
	$	(29,240	)	$	(20,692	)	$	(15,805	)

For the year ended April 30, 2020, the Company recorded a U.S. Federal income tax benefit of $124,000. For the year ended April 30, 2019, the Company recorded a U.S. Federal income tax expense of $124,000. Prior to fiscal year 2019, the company incurred net losses since inception and has not historically recorded a benefit or expense related to income taxes.

A reconciliation between the effective tax rates and statutory rates for the years ended April 30, is as follows:

	2020			2019			2018
Income tax benefit at U.S. federal statutory rate		21.0	%		21.0	%		30.4	%
Foreign rate differential		(1.6	)%		(0.9	)%		(4.3	)%
Nondeductible expenses - UK R&D credit		(12.1	)%		(5.9	)%		(16.3	)%
Other		(0.5	)%		(0.9	)%		(4.5	)%
Effect of change in tax rates		—			—			(3.6	)%
Globl Intangible Low-Taxed Income ("GILTI")		—			(7.6	)%		—
Valuation allowance		(6.6	)%		(6.3	)%		(1.7	)%
		0.2	%		(0.6	)%		—

The tax effect of significant temporary differences representing deferred tax assets and liabilities as of April 30, 2020 and 2019 is as follows (in thousands):

	2020			2019
Net operating loss (“NOL”) carryforwards	$	7,367		$	7,424
Other		2,162			968
Valuation allowance		(9,529	)		(8,392	)
Net deferred tax asset	$	—		$	—

Management of the Company has determined it is not more likely than not that the Company will recognize the benefits of net deferred tax assets, the majority of which are NOLs, and has provided a valuation allowance for the full amount of deferred tax assets as of as of April 30, 2020 and 2019, respectively. During the years ended April 30, 2020, 2019, and 2018 the valuation allowance changed by $1.1 million, $1.6 million and $1.0 million, respectively. Realization of deferred tax assets is dependent upon the generation of future taxable income.

As of April 30, 2020, the Company has NOL carryforwards for federal income taxes of $312,000 that begin to expire in 2024 and $1.7 million that can be carried forward indefinitely. The Company also has NOL carryforwards for state income taxes of $5.9 million that begin to expire in 2036 and NOL carryforwards for U.K. income taxes of $37.1 million that do not expire. The ability to utilize the Company’s domestic net operating losses is limited due to changes in ownership as defined by Section 382 of the Internal Revenue Code (the “Code”). Under the provisions of Sections 382 and 383 of the Code, a change of control, as defined in the Code, imposes an annual limitation on the amount of the Company’s net operating loss and tax credit carryforwards, and other tax attributes that can be used to reduce future tax liabilities. The Company determined that ownership changes occurred as a result of a transaction in November 2016 and a public offering in September 2018. As a result of these ownership changes, it is estimated that the effect of Section 382 will generally limit the amount of the net operating loss carryforwards that are available to offset future taxable income to approximately $5.0 million, annually.

The Company recognizes the financial statement effects of a tax position when it becomes more likely than not, based upon the technical merits, that the position will be sustained upon examination. The Company files U.S. Federal tax returns, as well as certain state returns. The Company also files returns in the United Kingdom. The Company is subject to U.S. Federal, state, and U.K. income tax examinations by authorities for tax years ending after 2015. There are currently no federal, state, or U.K. audits in process. Tax year 2016 and subsequent years contain matters that could be subject to differing interpretations of the applicable tax laws and regulations as it relates to the amount and or timing of income, deductions, and tax credits. Although the outcome of tax audits is always uncertain, management has analyzed the Company’s tax positions taken for all open tax years and has concluded that no provision for unrecognized tax benefits from uncertain tax positions is required in the Company’s consolidated financial statements for the years ended April 30, 2020 and 2019, respectively.

Defined Contribution Plans

12 Months Ended

Apr. 30, 2020

Compensation And Retirement Disclosure [Abstract]

Defined Contribution Plans

Note 11. Defined Contribution Plans

Participation in a personal pension plan is available to all U.K. based employees of the Company upon commencement of their employment. Employer contributions are made in accordance with the terms and conditions of the employment contract. Employees may contribute in accordance with the prevailing statutory limitations. Employees of the U.S. parent company are eligible to participate in the Company's 401(k) Plan. The Company matches up to 4% of employee contributions to the Plan. Total employer contributions to both plans for the years ended April 30, 2020, 2019 and 2018 were $314,000, $237,000 and $219,000 respectively.

Other Income

12 Months Ended

Apr. 30, 2020

Other Nonoperating Income Expense [Abstract]

Other Income

Note 12. Other Income

As of April 30, 2020 and 2019, the Company had research and development tax credits receivable totaling $16.5 million and $11.3 million, respectively. This tax credit is related to a tax scheme for small and medium enterprises in the United Kingdom as well as an R&D expenditure credit system that allows the Company to file a claim for cash credit in proportion to the Company’s R&D expenditure for the year. This amount is included in other income, as it is a refundable credit that does not depend on the Company’s ongoing tax status or position. The Company recognized $9.5 million, $7.6 million and $4.4 million related to these programs in the years ended April 30, 2020, 2019 and 2018, respectively. In the year ended April 30, 2020, other income also included $0.3 million of realized gains from the sale of available for sale securities.

Unaudited Quarterly Financial Information

12 Months Ended

Apr. 30, 2020

Quarterly Financial Information Disclosure [Abstract]

Unaudited Quarterly Financial Information

Note 13. Unaudited Quarterly Financial Information (in thousands):

Fiscal year 2020	Quarter ended July 31, 2019			Quarter ended October 31, 2019			Quarter ended January 31, 2020			Quarter ended April 30, 2020
Revenue	$	3,369		$	3,920		$	1,577		$	3,824
Operating expenses		12,933			13,209			14,301			12,781
Net loss		(7,338	)		(5,903	)		(9,291	)		(6,585	)
Net loss per share	$	(0.42	)	$	(0.33	)	$	(0.52	)	$	(0.37	)

Fiscal year 2019	Quarter ended July 31, 2018			Quarter ended October 31, 2018			Quarter ended January 31, 2019			Quarter ended April 30, 2019
Revenue	$	3,718		$	5,592		$	3,890		$	2,926
Operating expenses		10,727			10,485			10,550			14,186
Net loss		(5,030	)		(3,304	)		(3,956	)		(8,526	)
Net loss per share	$	(0.47	)	$	(0.22	)	$	(0.23	)	$	(0.49	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Apr. 30, 2020

Accounting Policies [Abstract]

Principles of Consolidation

Use of Estimates

Foreign Currency

Segment Reporting

Cash and Cash Equivalents

Research and Development Tax Credit Receivable

Property and Equipment

Asset Classification		Estimated Useful Life
Machinery and equipment		1-5 Years
Computer equipment		3-4 Years
Motor vehicles		4 Years
Leasehold improvements		5 Years or term of lease, if shorter

Revenue Recognition

Research and Development

Research and development: Research and development costs are expensed as incurred and include, but are not limited to:

•

Employee-related expenses including salaries, benefits, travel, and share-based compensation expense for research and development personnel;

•

Costs associated with preclinical and development activities;

•

Costs associated with regulatory operations.

Income Taxes

Stock Based Compensation

Net Loss per Share

Potential dilutive common share equivalents consist of:

	April 30,
	2020		2019		2018
Stock options and awards		2,320,677		1,784,338		388,366

Fair Value Measurement

The following tables summarize the cash equivalents and marketable securities measured at fair value on a recurring basis as of April 30, 2020 and 2019:

	Level 1		Level 2		Level 3		Balance at April 30, 2020
Cash equivalents	$	650	$	—	$	—	$	650
Marketable securities:
Corporate debt securities		—		39,216		—		39,216
U.S. government agency securities		—		12,709		—		12,709
	$	650	$	51,925	$	—	$	52,575

	Level 1		Level 2		Level 3		Balance at April 30, 2019
Cash equivalents	$	30,044	$	1,962	$	—	$	32,006
Marketable securities:
Corporate debt securities		—		56,487		—		56,487
U.S. government agency securities		—		12,318		—		12,318
	$	30,044	$	70,767	$	—	$	100,811

Recently Issued Accounting Pronouncements Adopted and Not Yet Adopted

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Apr. 30, 2020

Accounting Policies [Abstract]

Estimated Useful Life of Property and Equipment

Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which are as follows:

Asset Classification		Estimated Useful Life
Machinery and equipment		1-5 Years
Computer equipment		3-4 Years
Motor vehicles		4 Years
Leasehold improvements		5 Years or term of lease, if shorter

Schedule of Potential Dilutive Common Share Equivalents

Potential dilutive common share equivalents consist of:

	April 30,
	2020		2019		2018
Stock options and awards		2,320,677		1,784,338		388,366

Schedule of Cash Equivalents and Marketable Securities Measured at Fair Value

The following tables summarize the cash equivalents and marketable securities measured at fair value on a recurring basis as of April 30, 2020 and 2019:

	Level 1		Level 2		Level 3		Balance at April 30, 2020
Cash equivalents	$	650	$	—	$	—	$	650
Marketable securities:
Corporate debt securities		—		39,216		—		39,216
U.S. government agency securities		—		12,709		—		12,709
	$	650	$	51,925	$	—	$	52,575

	Level 1		Level 2		Level 3		Balance at April 30, 2019
Cash equivalents	$	30,044	$	1,962	$	—	$	32,006
Marketable securities:
Corporate debt securities		—		56,487		—		56,487
U.S. government agency securities		—		12,318		—		12,318
	$	30,044	$	70,767	$	—	$	100,811

Marketable Securities (Tables)

12 Months Ended

Apr. 30, 2020

Investments Debt And Equity Securities [Abstract]

Summary of Fair Value of Company's Investments By Type

The following tables summarize the fair value of the Company’s investments by type as of April 30, 2020 and 2019:

	April 30, 2020
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities	$	38,922	$	295	$	(1	)	$	39,216
Obligations of the U.S. Government and its agencies		12,534		175		—			12,709
Total investments	$	51,456	$	470	$	(1	)	$	51,925

	April 30, 2019
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities	$	56,083	$	405	$	(1	)	$	56,487
Obligations of the U.S. Government and its agencies		12,282		36		—			12,318
Total investments	$	68,365	$	441	$	(1	)	$	68,805

Summary of Scheduled Maturity for Investments

The following table summarizes the scheduled maturity for the Company’s investments at April 30, 2020:

	April 30,
	2020
Maturing in one year or less	$	32,391
Maturing after one year through two years		11,698
Maturing after two years		7,836
Total investments	$	51,925

Property and Equipment (Tables)

12 Months Ended

Apr. 30, 2020

Property Plant And Equipment [Abstract]

Components of Property and Equipment

At April 30, 2020 and 2019, property and equipment consisted of (in thousands):

	2020			2019
Laboratory equipment	$	1,543		$	1,391
Office equipment		36			36
Furniture & fixtures		185			175
Leasehold improvements		1,647			1,707
Total property and equipment at cost		3,411			3,309
Less: Accumulated depreciation		(1,368	)		(896	)
Property and equipment, net	$	2,043		$	2,413

Accrued Expenses (Tables)

12 Months Ended

Apr. 30, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

At April 30, 2020 and 2019, accrued expenses consisted of (in thousands):

	2020		2019
Accrued research expense	$	2,821	$	3,065
Accrued compensation		2,333		1,949
Accrued professional fees		173		186
Other accrued expenses		128		447
Total accrued expenses	$	5,455	$	5,647

Stock-Based Compensation (Tables)

12 Months Ended

Apr. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Fair Value of Share-based Awards Measured with Weighted-Average Assumptions

The fair value of the share-based awards was measured with the following weighted-average assumptions for the fiscal years ended April 30:

	2020	2019	2018
Risk-free interest rate	2.06	2.90	1.94
Expected life of the options	6.25 years	6.25 years	6.25 years
Expected volatility of the underlying stock	81.1%	77.2%	76.9%
Expected dividend rate	0%	0%	0%

Schedule of Stock-Based Compensation Expense

Stock-based compensation was reflected in the Company’s consolidated statement of operations and comprehensive loss as follows (in thousands):

	Year ended April 30,
	2020		2019		2018
Research and development	$	1,944	$	2,005	$	320
General and administrative		2,504		961		740
Total stock-based compensation expense	$	4,448	$	2,966	$	1,060

Summary of Option Activity

A summary of option activity for the year ended April 30, 2020 and changes during the years then ended is presented below:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
Outstanding at May 1, 2019		1,739,338		$	9.95		8.47	$	22,807
Exercised		(37,494	)		4.39
Granted		586,500			22.90
Cancelled		(12,667	)		19.89
Outstanding at April 30, 2020		2,275,677		$	13.32		7.83	$	4,899
Exercisable at April 30, 2020		1,157,171		$	9.73		7.25	$	3,931
Vested and expected to vest at April 30, 2020		2,275,677		$	13.32		7.83	$	4,899

Leases (Tables)

12 Months Ended

Apr. 30, 2020

Leases [Abstract]

Summary of Lease Costs

The following table summarizes lease costs included in research and development and general and administrative expense for the year ended April 30, 2020 (in thousands):

	Year Ended
	April 30, 2020
Operating lease costs	$	743
Finance lease costs		54
Short-term lease costs		13
Variable lease costs		47
Total lease costs	$	857

Summary of Maturity of Undiscounted Payments Due Under Lease Liabilities and Present Value of Liabilities

The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of April 30, 2020 (in thousands):

Years ending April 30,	Operating Leases
2021	$	679
2022		383
2023		239
2024		142
2025		142
Thereafter		439
Total lease payments		2,024
Less: imputed interest	379
Total lease liabilities		1,645
Current lease liabilities	588
Long-term lease liabilities	$	1,057

Schedule of Future Minimum Payments Under Finance and Operating Leases

Future minimum payments under these leases as of April 30, 2019 are as follows (in thousands):

Years ending April 30,	Finance Leases		Operating Leases
2020	$	54	$	687
2021		—		474
2022		—		328
2023		—		194
2024 and thereafter		—		495
Total minimum lease payments	$	54	$	2,178
Less amounts representing interest		—
Present Value of minimum payments		54
Current portion		54
Long-term portion	$	—

Summary of Lease Term and Discount Rate

The following table summarizes the lease term and discount rate as of April 30, 2020:

	April 30, 2020
Weighted-average remaining lease term (years)
Operating leases	4.8
Weighted-average discount rate
Operating leases		9.0	%

Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the year ended April 30, 2020 (in thousands):

	April 30, 2020
Cash paid for amounts included in the measurement of operating lease liabilities	$	708
Cash paid for amounts included in the measurement of finance lease liabilities	$	54

Income Taxes (Tables)

12 Months Ended

Apr. 30, 2020

Income Tax Disclosure [Abstract]

Schedule of Components of the Company's Loss Before Income Taxes

The components of the Company’s loss before income taxes for the years ended April 30, 2020, 2019 and 2018 consisted of the following (in thousands):

	2020			2019			2018
Domestic	$	(6,337	)	$	(5,006	)	$	(4,020	)
Foreign		(22,903	)		(15,686	)		(11,785	)
	$	(29,240	)	$	(20,692	)	$	(15,805	)

Schedule of Reconciliation between Effective Tax Rates and Statutory Rates

A reconciliation between the effective tax rates and statutory rates for the years ended April 30, is as follows:

	2020			2019			2018
Income tax benefit at U.S. federal statutory rate		21.0	%		21.0	%		30.4	%
Foreign rate differential		(1.6	)%		(0.9	)%		(4.3	)%
Nondeductible expenses - UK R&D credit		(12.1	)%		(5.9	)%		(16.3	)%
Other		(0.5	)%		(0.9	)%		(4.5	)%
Effect of change in tax rates		—			—			(3.6	)%
Globl Intangible Low-Taxed Income ("GILTI")		—			(7.6	)%		—
Valuation allowance		(6.6	)%		(6.3	)%		(1.7	)%
		0.2	%		(0.6	)%		—

Schedule of Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities

The tax effect of significant temporary differences representing deferred tax assets and liabilities as of April 30, 2020 and 2019 is as follows (in thousands):

	2020			2019
Net operating loss (“NOL”) carryforwards	$	7,367		$	7,424
Other		2,162			968
Valuation allowance		(9,529	)		(8,392	)
Net deferred tax asset	$	—		$	—

Unaudited Quarterly Financial Information (Tables)

12 Months Ended

Apr. 30, 2020

Quarterly Financial Information Disclosure [Abstract]

Summary of Unaudited Quarterly Financial Information

Fiscal year 2020	Quarter ended July 31, 2019			Quarter ended October 31, 2019			Quarter ended January 31, 2020			Quarter ended April 30, 2020
Revenue	$	3,369		$	3,920		$	1,577		$	3,824
Operating expenses		12,933			13,209			14,301			12,781
Net loss		(7,338	)		(5,903	)		(9,291	)		(6,585	)
Net loss per share	$	(0.42	)	$	(0.33	)	$	(0.52	)	$	(0.37	)

Fiscal year 2019	Quarter ended July 31, 2018			Quarter ended October 31, 2018			Quarter ended January 31, 2019			Quarter ended April 30, 2019
Revenue	$	3,718		$	5,592		$	3,890		$	2,926
Operating expenses		10,727			10,485			10,550			14,186
Net loss		(5,030	)		(3,304	)		(3,956	)		(8,526	)
Net loss per share	$	(0.47	)	$	(0.22	)	$	(0.23	)	$	(0.49	)

Description of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ 121,592	$ 92,476
Cash, cash equivalents and marketable securities	$ 67,700

Summary of Significant Accounting Policies - Estimated Useful Life of Property and Equipment (Detail)	12 Months Ended
	Apr. 30, 2020
Machinery and Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	1 year
Machinery and Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	5 years
Computer Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	3 years
Computer Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	4 years
Motor Vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	4 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	5 Years or term of lease, if shorter

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018	May 01, 2019
Summary of Significant Accounting Policies [Line Items]
Uncertain tax positions	$ 0	$ 0	$ 0
Interest or penalties charges recognized	0	$ 0	$ 0
Operating lease assets	1,612,000
Operating lease liabilities	$ 1,645,000
Topic 842 [Member]
Summary of Significant Accounting Policies [Line Items]
Operating lease assets				$ 1,900,000
Operating lease liabilities				$ 1,900,000

Summary of Significant Accounting Policies - Schedule of Potential Dilutive Common Share Equivalents (Detail) - shares	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Stock Options and Awards [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive potential common share equivalents outstanding	2,320,677	1,784,338	388,366

Summary Of Significant Accounting Policies - Schedule of Cash Equivalents and Marketable Securities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 650	$ 32,006
Cash equivalents and marketable securities	52,575	100,811
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	650	30,044
Cash equivalents and marketable securities	650	30,044
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		1,962
Cash equivalents and marketable securities	51,925	70,767
Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	39,216	56,487
Corporate Debt Securities [Member] \| Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	39,216	56,487
U.S. Government Agency Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	12,709	12,318
U.S. Government Agency Securities [Member] \| Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 12,709	$ 12,318

Marketable Securities - Summary of Fair Value of Company's Investment By Type (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 51,456	$ 68,365
Unrealized Gains	470	441
Unrealized Losses	(1)	(1)
Fair Value	51,925	68,805
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	38,922	56,083
Unrealized Gains	295	405
Unrealized Losses	(1)	(1)
Fair Value	39,216	56,487
Obligations of U.S. Government and Its Agencies [Member]
Marketable Securities [Line Items]
Amortized Cost	12,534	12,282
Unrealized Gains	175	36
Fair Value	$ 12,709	$ 12,318

Marketable Securities - Summary of Scheduled Maturity for Investments (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Investments Debt And Equity Securities [Abstract]
Maturing in one year or less	$ 32,391
Maturing after one year through two years	11,698
Maturing after two years	7,836
Total investments	$ 51,925	$ 68,805

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	$ 3,411	$ 3,309
Less: Accumulated depreciation	(1,368)	(896)
Property and equipment, net	2,043	2,413
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	1,543	1,391
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	36	36
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	185	175
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	$ 1,647	$ 1,707

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 512	$ 378	$ 180

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Payables And Accruals [Abstract]
Accrued research expense	$ 2,821	$ 3,065
Accrued compensation	2,333	1,949
Accrued professional fees	173	186
Other accrued expenses	128	447
Total accrued expenses	$ 5,455	$ 5,647

Merck Arrangement - Additional Information (Detail) $ in Millions		1 Months Ended	12 Months Ended
	Oct. 06, 2017 PerformanceObligation	Nov. 30, 2017 USD ($)	Apr. 30, 2020 USD ($)	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($)
Research and Development Services for KVD001 and Oral DME [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of performance obligations \| PerformanceObligation	2
Merck [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			$ 12.7	$ 16.1	$ 8.0
Merck [Member] \| Remaining Unsatisfied Performance Obligations [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 3.8
KalVista Pharmaceuticals Limited [Member] \| Merck [Member] \| Option Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement commencement date			Oct. 06, 2017
Non-refundable upfront fee		$ 37.0

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2020 USD ($) Plan $ / shares shares	Apr. 30, 2019 USD ($) $ / shares	Apr. 30, 2018 USD ($) $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of equity-based compensation plans \| Plan	3
Number of legacy plans \| Plan	2
Weighted-average grant date fair value of stock options granted \| $ / shares	$ 15.76	$ 9.62	$ 4.87
Total intrinsic value of stock options exercised \| $	$ 431,000	$ 950,000	$ 131,000
Total cash received as a result of employee stock option exercises \| $	216,000	$ 242,000	$ 36,000
Unrecognized compensation expense related to unvested awards \| $	$ 10,200
Unrecognized compensation expense related to unvested awards expected to be recognized over a weighted-average period	2 years 3 months 18 days
2017 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, available for grant \| shares	942,122
Common stock reserved for issuance upon exercise or settlement of stock options or other awards \| shares	3,538,090
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grants vest percentage	25.00%
Recurring grants vesting period	4 years
Scheme termination period	10 years
Stock Options [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted, vesting period	1 year
Stock Options [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted, vesting period	3 years
Performance Based Restricted Stock Unit [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance-based restricted stock unit awards outstanding \| shares	45,000
Performance period expiration date	Jun. 30, 2022

Stock-Based Compensation - Schedule of Fair Value of Share-based Awards Measured with Weighted-Average Assumptions (Detail)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.06%	2.90%	1.94%
Expected life of the options	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility of the underlying stock	81.10%	77.20%	76.90%
Expected dividend rate	0.00%	0.00%	0.00%

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 4,448	$ 2,966	$ 1,060
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,944	2,005	320
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,504	$ 961	$ 740

Stock-Based Compensation - Summary of Option Activity (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding Beginning Balance	1,739,338
Shares, Exercised	(37,494)
Shares, Granted	586,500
Shares, Cancelled	(12,667)
Shares, Outstanding Ending Balance	2,275,677	1,739,338
Shares, Exercisable	1,157,171
Shares, Vested and expected to vest	2,275,677
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 9.95
Weighted Average Exercise Price, Exercised	4.39
Weighted Average Exercise Price, Granted	22.90
Weighted Average Exercise Price, Cancelled	19.89
Weighted Average Exercise Price, Outstanding Ending Balance	13.32	$ 9.95
Weighted Average Exercise Price, Exercisable	9.73
Weighted Average Exercise Price, Vested and expected to vest	$ 13.32
Weighted Average Remaining Contractual Life, Outstanding	7 years 9 months 29 days	8 years 5 months 19 days
Weighted Average Remaining Contractual Life, Exercisable	7 years 3 months
Weighted Average Remaining Contractual Life, Vested and expected to vest	7 years 9 months 29 days
Aggregate Intrinsic Value, Outstanding Beginning Balance	$ 22,807
Aggregate Intrinsic Value, Outstanding Ending Balance	4,899	$ 22,807
Aggregate Intrinsic Value, Exercisable	3,931
Aggregate Intrinsic Value, Vested and expected to vest	$ 4,899

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Other Commitments [Line Items]
Contractual obligation remaining commitments including cancellation provisions	$ 3,600,000
Amounts associated with indemnifications	0
Maximum [Member]
Other Commitments [Line Items]
Royalty payable upon completion of first commercial sale	$ 1,000,000
Royalty payment obligations expiration period	90 days
Indemnification Guarantee [Member]
Other Commitments [Line Items]
Contingent liabilities	$ 0	$ 0

Leases - Additional Information (Detail)	12 Months Ended
Leases - Additional Information (Detail)	Apr. 30, 2020 USD ($) ft²	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($) ft²	Feb. 29, 2020 ft²
General and Administrative Expenses and Research and Development Expenses [Member]
Lessee Lease Description [Line Items]
Rent expense \| $	$ 743,000	$ 677,000	$ 638,000
Massachusetts [Member]
Lessee Lease Description [Line Items]
Lease agreement square feet	2,700
Lessee, lease term	5 years
United Kingdom [Member]
Lessee Lease Description [Line Items]
Lease agreement square feet			8,800	4,600
Lessee, lease term			10 years	8 years

Leases - Summary of Lease Costs (Detail) $ in Thousands	12 Months Ended
Leases - Summary of Lease Costs (Detail) $ in Thousands	Apr. 30, 2020 USD ($)
Lease Cost [Abstract]
Operating lease costs	$ 743
Finance lease costs	54
Short-term lease costs	13
Variable lease costs	47
Total lease costs	$ 857

Leases - Summary of Maturity of Undiscounted Payments Due Under Lease Liabilities and Present Value of Liabilities (Detail) $ in Thousands	Apr. 30, 2020 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2021	$ 679
2022	383
2023	239
2024	142
2025	142
Thereafter	439
Total lease payments	2,024
Less: imputed interest	379
Total lease liabilities	1,645
Current lease liabilities	588
Long-term lease liabilities	$ 1,057

Leases - Schedule of Future Minimum Payments Under Finance and Operating Leases (Detail) $ in Thousands	Apr. 30, 2019 USD ($)
Finance Leases
2020	$ 54
Total minimum lease payments	54
Present Value of minimum payments	54
Current portion	54
Operating Leases
2020	687
2021	474
2022	328
2023	194
2024 and thereafter	495
Total minimum lease payments	$ 2,178

Leases - Summary of Lease Term and Discount Rate (Detail)	Apr. 30, 2020
Lease Cost [Abstract]
Operating lease, Weighted-average remaining lease term (years)	4 years 9 months 18 days
Operating lease, Weighted-average discount rate	9.00%

Leases - Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities (Detail) $ in Thousands	12 Months Ended
	Apr. 30, 2020 USD ($)
Lease Cost [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities	$ 708
Cash paid for amounts included in the measurement of finance lease liabilities	$ 54

Income Taxes - Schedule of Components of the Company's Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (6,337)	$ (5,006)	$ (4,020)
Foreign	(22,903)	(15,686)	(11,785)
Income before income taxes	$ (29,240)	$ (20,692)	$ (15,805)

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ (124,000)	$ 124,000
Change in valuation allowance	1,100,000	1,600,000	$ 1,000,000
NOL carryforwards	5,000,000
Provision for unrecognized tax benefits	0	$ 0	$ 0
Federal Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	312,000
Federal Income Tax [Member] \| Carried Forward Indefinitely [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 1,700,000
Federal Income Tax [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2024
State Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 5,900,000
State Income Tax [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2036
U.K. Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 37,100,000

Income Taxes - Schedule of Reconciliation between Effective Tax Rates and Statutory Rates (Detail)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Income tax benefit at U.S. federal statutory rate	21.00%	21.00%	30.40%
Foreign rate differential	(1.60%)	(0.90%)	(4.30%)
Nondeductible expenses - UK R&D credit	(12.10%)	(5.90%)	(16.30%)
Other	(0.50%)	(0.90%)	(4.50%)
Effect of change in tax rates			(3.60%)
Globl Intangible Low-Taxed Income ("GILTI")		(7.60%)
Valuation allowance	(6.60%)	(6.30%)	(1.70%)
Effective income tax rate	0.20%	(0.60%)

Income Taxes - Schedule of Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Income Tax Disclosure [Abstract]
Net operating loss (“NOL”) carryforwards	$ 7,367	$ 7,424
Other	2,162	968
Valuation allowance	$ (9,529)	$ (8,392)

Defined Contribution Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
U.S. Employees 401(K) Plan [Member] \| Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of employee contributions matched to the plan	4.00%
U.K. Employees Personal Pension Plan and U.S. Employees 401(K) Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Total employer contributions	$ 314,000	$ 237,000	$ 219,000

Other Income - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Other Nonoperating Income Expense [Line Items]
Research and development tax credits receivable	$ 16,527	$ 11,315
Other Income [Member]
Other Nonoperating Income Expense [Line Items]
Realized gains from sale of available for sale securities	300
Research and Development Tax Credits [Member]
Other Nonoperating Income Expense [Line Items]
Revenue recognized	$ 9,500	$ 7,600	$ 4,400

Unaudited Quarterly Financial Information - Summary of Unaudited Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,824	$ 1,577	$ 3,920	$ 3,369	$ 2,926	$ 3,890	$ 5,592	$ 3,718	$ 12,690	$ 16,127	$ 8,394
Operating expenses	12,781	14,301	13,209	12,933	14,186	10,550	10,485	10,727	53,223	45,947	27,099
Net loss	$ (6,585)	$ (9,291)	$ (5,903)	$ (7,338)	$ (8,526)	$ (3,956)	$ (3,304)	$ (5,030)	$ (29,116)	$ (20,816)	$ (15,805)
Net loss per share	$ (0.37)	$ (0.52)	$ (0.33)	$ (0.42)	$ (0.49)	$ (0.23)	$ (0.22)	$ (0.47)	$ (1.64)	$ (1.38)	$ (1.53)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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