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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Apr. 30, 2017	Jul. 01, 2017	Oct. 31, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Apr. 30, 2017
Document Fiscal Year Focus	2017
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 Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		9,713,042
Entity Public Float			$ 11,607,447

Consolidated Balance Sheets - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Current assets:
Cash and cash equivalents	$ 30,950	$ 21,764
Research and development tax credit receivable	2,250	1,883
Grants receivable	297	356
Prepaid expenses and other current assets	751	668
Total current assets	34,248	24,671
Property and equipment, net	97	74
Total assets	34,345	24,745
Current liabilities:
Accounts payable	1,153	1,008
Accrued expenses	1,865	2,114
Due to related parties		127
Total current liabilities	3,018	3,249
Commitments and contingencies (Note 10)
Convertible Preferred Stock		58,608
Stockholders’ equity (deficit):
Ordinary Shares, $0.0016 par value Shares issued and outstanding: None at April 30, 2017 and 2,167,367 at April 30, 2016		3
Common stock, $0.001 par value Shares authorized: 100,000,000 at April 30, 2017 Shares issued and outstanding: 9,713,042 at April 30, 2017 and none at April 30, 2016	10
Additional paid-in capital	89,815	212
Accumulated deficit	(55,855)	(37,252)
Accumulated other comprehensive loss	(2,643)	(75)
Total stockholders’ equity (deficit)	31,327	(37,112)
Total liabilities and stockholders’ equity (deficit)	$ 34,345	24,745
Series B Convertible Preferred Stock [Member]
Current liabilities:
Convertible Preferred Stock		33,002
Series A Convertible Preferred Stock [Member]
Current liabilities:
Convertible Preferred Stock		$ 25,606

Consolidated Balance Sheets (Parenthetical) - $ / shares	Apr. 30, 2017	Apr. 30, 2016
Ordinary shares, par value	$ 0.0016	$ 0.0016
Ordinary shares, issued	0	2,167,367
Ordinary shares, outstanding	0	2,167,367
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000
Common stock, shares issued	9,713,042	0
Common stock, shares outstanding	9,713,042	0
Series B Convertible Preferred Stock [Member]
Convertible preferred stock, par value	$ 0.0016	$ 0.0016
Convertible preferred stock, shares issued	0	8,422,898
Convertible preferred stock, shares outstanding	0	8,422,898
Series A Convertible Preferred Stock [Member]
Convertible preferred stock, par value	$ 0.0016	$ 0.0016
Convertible preferred stock, shares issued	0	15,900,000
Convertible preferred stock, shares outstanding	0	15,900,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Income Statement [Abstract]
Grant income	$ 1,504,000	$ 2,133,000	$ 1,804,000
Operating expenses:
Research and development expenses	12,666,000	14,661,000	8,285,000
General and administrative expenses	11,177,000	2,653,000	1,608,000
Total operating expenses	23,843,000	17,314,000	9,893,000
Operating loss	(22,339,000)	(15,181,000)	(8,089,000)
Other income:
Interest income	36,000	50,000	19,000
Foreign currency exchange rate gain	1,371,000	1,661,000
Other income	2,329,000	2,034,000	844,000
Total other income	3,736,000	3,745,000	863,000
Net loss	(18,603,000)	(11,436,000)	(7,226,000)
Other comprehensive income (loss):
Foreign currency translation adjustments	(2,568,000)	(2,240,000)	(156,000)
Comprehensive loss	$ (21,171,000)	$ (13,676,000)	$ (7,382,000)
Net loss per share attributable to common stockholders, basic and diluted	$ (4.47)	$ (26.17)	$ (34.94)
Weighted average common shares outstanding, basic and diluted	4,646,764	591,298	263,358

Consolidated Statements of Changes in Convertible Preferred Shares and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Ordinary Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	KALVISTA PHARMACEUTICALS, INC. [Member]	KALVISTA PHARMACEUTICALS, INC. [Member] Ordinary Shares [Member]	KALVISTA PHARMACEUTICALS, INC. [Member] Common Stock [Member]	KALVISTA PHARMACEUTICALS, INC. [Member] Additional Paid-in Capital [Member]	Series B Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member] KALVISTA PHARMACEUTICALS, INC. [Member]	Series A Convertible Preferred Stock [Member]	Series A Convertible Preferred Stock [Member] KALVISTA PHARMACEUTICALS, INC. [Member]	Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member] KALVISTA PHARMACEUTICALS, INC. [Member]
Balance at Apr. 30, 2014													$ 16,913		$ 16,913
Balance, shares at Apr. 30, 2014													10,500,000		10,500,000
Balance at Apr. 30, 2014	$ (16,210)	$ 1		$ 58	$ (18,590)	$ 2,321
Balance, shares at Apr. 30, 2014		526,050
Issuance of convertible preferred stock net of issuance costs													$ 8,693		$ 8,693
Issuance of convertible preferred stock net of issuance costs, shares													5,400,000		5,400,000
Issuance of ordinary shares	1	$ 1
Issuance of ordinary shares, shares		776,317
Stock-based compensation expense	36			36
Net loss	(7,226)				(7,226)
Foreign currency translation adjustments	(156)					(156)
Balance at Apr. 30, 2015													$ 25,606		$ 25,606
Balance, shares at Apr. 30, 2015													15,900,000		15,900,000
Balance at Apr. 30, 2015	(23,555)	$ 2		94	(25,816)	2,165
Balance, shares at Apr. 30, 2015		1,302,367
Issuance of convertible preferred stock net of issuance costs											$ 33,002				$ 33,002
Issuance of convertible preferred stock net of issuance costs, shares											8,422,898				8,422,898
Issuance of ordinary shares	1	$ 1
Issuance of ordinary shares, shares		865,000
Stock-based compensation expense	118			118
Net loss	(11,436)				(11,436)
Foreign currency translation adjustments	(2,240)					(2,240)
Balance at Apr. 30, 2016	58,608										$ 33,002		$ 25,606		$ 58,608
Balance, shares at Apr. 30, 2016											8,422,898		15,900,000		24,322,898
Balance at Apr. 30, 2016	(37,112)	$ 3		212	(37,252)	(75)
Balance, shares at Apr. 30, 2016		2,167,367
Issuance of ordinary shares	2	$ 2
Issuance of ordinary shares, shares		396,719
Transaction, value												$ (33,002)		$ (25,606)		$ (58,608)
Transaction, shares												(8,422,898)		(15,900,000)		(24,322,898)
Transaction, value							$ 89,214	$ (5)	$ 10	$ 89,209
Transaction, shares								(2,564,086)	9,713,042
Stock-based compensation expense	394			394
Net loss	(18,603)				(18,603)
Foreign currency translation adjustments	(2,568)					(2,568)
Balance, shares at Apr. 30, 2017											0		0
Balance at Apr. 30, 2017	$ 31,327		$ 10	$ 89,815	$ (55,855)	$ (2,643)
Balance, shares at Apr. 30, 2017			9,713,042

Consolidated Statements of Changes in Convertible Preferred Shares and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Series A Convertible Preferred Stock [Member]
Stock issuance costs		$ 6
Series B Convertible Preferred Stock [Member]
Stock issuance costs	$ 186

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Cash flows from operating activities:
Net loss	$ (18,603,000)	$ (11,436,000)	$ (7,226,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	40,000	33,000	38,000
Share-based compensation expense	394,000	118,000	36,000
Foreign currency exchange rate gain	(1,371,000)	(1,661,000)
Changes in operating assets and liabilities, net of changes from business acquired:
Research and development tax credit receivable	(600,000)	(1,148,000)	(94,000)
Grants receivable	29,000	(137,000)	65,000
Prepaid expenses and other current assets	(81,000)	(475,000)	210,000
Accounts payable	(1,599,000)	374,000	167,000
Accrued expenses	(1,931,000)	1,176,000	436,000
Net cash used in operating activities	(23,722,000)	(13,156,000)	(6,368,000)
Cash flows from investing activities:
Cash acquired in Carbylan transaction	34,139,000
Purchases of property and equipment	(74,000)	(11,000)	(125,000)
Net cash provided by (used in) investing activities	34,065,000	(11,000)	(125,000)
Cash flows from financing activities:
Proceeds from issuance of common stock	2,000	1,000	1,000
Net cash provided by financing activities	2,000	33,003,000	8,662,000
Effect of exchange rate changes on cash	(1,159,000)	(598,000)	(124,000)
Net increase in cash and cash equivalents	9,186,000	19,238,000	2,045,000
Cash and cash equivalents, beginning year	21,764,000	2,526,000	481,000
Cash and cash equivalents, end of year	30,950,000	21,764,000	2,526,000
Supplemental disclosures of cash flow information:
Conversion of preferred stock and ordinary shares to common stock	$ 58,613,000
Series A Preferred Stock [Member]
Cash flows from financing activities:
Proceeds from issuance of Preferred Stock, net of issuance costs			$ 8,661,000
Series B Preferred Stock [Member]
Cash flows from financing activities:
Proceeds from issuance of Preferred Stock, net of issuance costs		$ 33,002,000

Description of Business, Basis of Presentation and Going Concern	12 Months Ended
	Apr. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business, Basis of Presentation and Going Concern	Note 1. Description of Business, Basis of Presentation and Going Concern KalVista Pharmaceuticals, Inc. (the “Company” or “KalVista”) is a clinical-stage pharmaceutical company focused on the discovery, development and commercialization of small molecule serine protease inhibitors as new treatments for diseases with significant unmet need. The Company’s initial focus is on developing a portfolio of oral inhibitors of plasma kallikrein for two indications: hereditary angioedema, or HAE, and diabetic macular edema or DME. The first oral program, KVD818, is currently in Phase 1 clinical testing and additional programs are in preclinical development. KalVista also has developed an intravitreally administered plasma kallikrein inhibitor for DME that has completed a Phase 1 clinical trial and is anticipated to commence Phase 2 testing later in 2017. The Company’s headquarters is located in Cambridge, Massachusetts, and the Company operates a research facility in the United Kingdom. On November 21, 2016 KalVista Pharmaceuticals Limited (“KalVista Limited”) completed a share purchase transaction with Carbylan Therapeutics Inc. (“Carbylan”) in an all-stock transaction whereby immediately following the transaction Carbylan’s equity holders owned 19% and KalVista Limited’s equity holders owned 81% of the combined company, respectively (see Note 6). As a result, Carbylan issued approximately 7.8 million shares of common stock to the stockholders of KalVista Limited in exchange for their common shares of KalVista Limited. Approximately 1.9 million shares were retained by the Carbylan stockholders. The combined company was renamed KalVista Pharmaceuticals, Inc. following the transaction. Following the completion of the transaction, the business being conducted by the Company became primarily the business conducted by KalVista Limited. As discussed in Note 6, KalVista Limited was identified as the acquirer for accounting purposes. The Company’s financial statement presentation reflects the business of KalVista Limited for periods prior to November 21, 2016 and the combined results of operations of KalVista Limited and Carbylan for the periods thereafter. The results of operations of the Carbylan business in the periods subsequent to acquisition date are not material. 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 business and financial statements of the Company. The Company has never been profitable and has not yet commenced commercial operations. KalVista 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 preferred stock and grant income. As of April 30, 2017, the Company had an accumulated deficit of $55.9 million and cash and cash equivalents totaling $31.0 million. Management believes that the cash and cash equivalents at April 30, 2017 will be able to fund 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 it becomes 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 business and prospects.

Summary of Significant Accounting Policies

12 Months Ended

Apr. 30, 2017

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. 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 foreign subsidiary is the Great Britain 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 the only component of the accumulated other comprehensive loss. In addition, the Company’s foreign subsidiary engages in transactions 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 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.

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 has primarily generated grant income for the development and commercialization of product candidates through sponsored research arrangements with non-profit organizations and from federal research and development grant programs. The Company recognizes revenue when amounts are realized or realizable and earned. Revenue is considered realizable and earned when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the price is fixed or determinable; and (4) collection of the amounts due are reasonably assured. See Note 8.

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: The Company uses the asset and liability method for accounting for income taxes. 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 both 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.

Net Loss per Share Attributable to Common Shareholders: Basic and diluted net loss per share is presented in conformity with the two-class method required for participating securities. Under the two-class method, basic net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Net loss attributable to common stockholders is determined by allocating undistributed earnings between holders of common and convertible preferred shares, based on the contractual dividend rights contained in the preferred share agreement. Where there is an undistributed loss, no amount is allocated to the convertible preferred shares. Diluted net loss per share is computed by dividing net loss by the sum of the weighted average number of common stock and the number of dilutive potential common stock equivalents outstanding during the period. Potential dilutive common share equivalents consist of the incremental common shares issuable upon the exercise of vested share options or the conversion of preferred stock.

Potential dilutive common share equivalents consist of:

	April 30,
	2017		2016		2015
Preferred stock		—		24,322,898		24,322,898
Stock options		148,469		76,643		62,424

In computing diluted earnings per share, common stock equivalents are not considered in periods in which a net loss is reported, as the inclusion of the common stock 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 (in thousands, except share and per share amounts).

Basic and diluted net loss per share	April 30,
	2017			2016			2015
Net loss	$	(18,603	)	$	(11,436	)	$	(7,226	)
Less: dividend on Series A		(935	)		(1,918	)		(1,977	)
Less: dividend on Series B		(1,237	)		(2,121	)		—
Loss available to common stockholders		(20,775	)		(15,475	)		(9,203	)
Weighted average common shares, basic and diluted		4,646,764			591,298			263,358
Net loss per share, basic and diluted	$	(4.47	)	$	(26.17	)	$	(34.94	)

The weighted average shares outstanding, reported loss per share and potential dilutive common share equivalents for the periods prior to November 21, 2016, the date of the Carbylan transaction, have been retrospectively adjusted to reflect historical weighted-average number of common shares outstanding multiplied by the exchange ratio established in the share purchase agreement.

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.

The Company’s financial instruments as of April 30, 2017 and 2016 consisted primarily of cash and cash equivalents, grants receivable and accounts payable. The carrying amount of these assets and liabilities approximate fair value given the short term maturity of these instruments.

Correction: The statements of operations and comprehensive loss for the years ended April 30, 2016 and 2015 have been restated to correct errors in the foreign currency translation adjustments which were reported as a gain rather than a loss and to correct the resulting summation of comprehensive loss. As a result of the correction of these errors, the total comprehensive loss for the year ended April 30, 2016 increased from a loss of $9,196,000 to a loss of $13,676,000, and the total comprehensive loss for the year ended April 30, 2015 increased from a loss of $7,070,000 to a loss of $7,382,000. There is no impact on the Company’s previously reported net loss, the balance sheet, the statement of changes in convertible preferred shares and stockholders’ equity (deficit) or the statement of cash flows for any period.

Recently issued accounting pronouncements not yet adopted: In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards update (“ASU”) 2014-09, “Revenue from Contracts with Customers,” requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The updated standard will replace most existing revenue recognition guidance in US GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. In July 2015, the FASB voted to defer the effective date for annual reporting periods beginning after December 15, 2017 (including interim reporting periods within those periods) and permitted early adoption of the standard, but not before the original effective date of December 15, 2016. The Company expects to adopt the updated standard in the first quarter of fiscal 2019 using the modified retrospective method of adoption. The Company is assessing the impact that adoption of this new guidance will have on the consolidated financial statements.

In February 2016, the FASB issued new lease accounting guidance in ASU No. 2016-02, “Leases” (Topic 842). Under the new guidance, lessees will be required to recognize for all leases (with the exception of short-term leases) at the commencement date: (1) a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and (2) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The new lease guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted, however, the Company does not intend to early adopt. The Company is assessing the impact that adoption of this new guidance will have on the consolidated financial statements.

In March 2016, the FASB issued ASU No. 2016-09, “Compensation – Stock Compensation” (“ASU 2016-09”) to require changes to several areas of employee share-based payment accounting in an effort to simplify share-based reporting. The update revises requirements in the following areas: minimum statutory withholding, accounting for income taxes and forfeitures. ASU 2016-09 is effective for annual reporting periods beginning after December 15, 2016. The Company is currently evaluating the impact that the adoption of this guidance may have on the consolidated financial statements.

In November 2016 the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230), Restricted Cash” (“ASU 2016-18”). The new standard requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The standard is effective for annual periods beginning after December 15, 2017, and interim periods within those annual reporting periods. Early adoption is permitted. The Company is currently evaluating the impact of this update on the consolidated financial statements.

In August 2016, the FASB issued ASU 2016-15, “Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments” (“ASU 2016-15”). The amendments in this update clarify how entities should classify certain cash receipts and cash payments on the Consolidated Statements of Cash Flows. The new guidance also clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. ASU 2016-15 will be effective for annual periods beginning after December 15, 2017, including interim periods within those annual reporting periods, but early adoption is permitted. The Company is currently evaluating the impact of this update on the consolidated financial statements.

Recently adopted accounting pronouncements

In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements—Going Concern,” on disclosure of uncertainties about an entity’s ability to continue as a going concern. This guidance addresses management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and to provide related footnote disclosures. The Company adopted this standard in its fiscal year ended April 30, 2017.

Property and Equipment

12 Months Ended

Apr. 30, 2017

Property Plant And Equipment [Abstract]

Property and Equipment

Note 3. Property and Equipment

At April 30, 2017 and 2016, property and equipment consisted of (in thousands):

	2017			2016
Laboratory equipment	$	373		$	358
Office equipment		31			58
Furniture & Fixtures		6			2
		410			418
Less accumulated depreciation		(313	)		(344	)
	$	97		$	74

For the years ended April 30, 2017, 2016 and 2015, depreciation expense was $40,000, $33,000 and $38,000, respectively.

Accrued Expenses

12 Months Ended

Apr. 30, 2017

Payables And Accruals [Abstract]

Accrued Expenses

Note 4. Accrued Expenses

At April 30, 2017 and 2016, accrued expenses consisted of (in thousands):

	2017		2016
Accrued research expense	$	348	$	1,059
Accrued compensation		1,300		966
Accrued professional fees		146		60
Other accrued expenses		71		29
	$	1,865	$	2,114

Related Party Transactions	12 Months Ended
Related Party Transactions	Apr. 30, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Note 5. Related Party Transactions On May 23, 2011, the Company entered into a sale and purchase agreement with Vantia Limited whereby, in return for a consideration of 500,000 Series A Preferred Shares in the Company at a subscription price of $1.61 per share, Vantia Limited transferred certain intellectual property and other business assets to the Company. Certain employees of Vantia Limited were also transferred to the Company as part of this transaction and the two entities shared common directors. On May 23, 2011, the Company entered into an agreement with Vantia Limited. The Company continued to pay Vantia for management fees and related expenses, which consist primarily of the cost of two Vantia employees who perform services for the Company and other administrative expenses. During the years ended April 30, 2017, 2016 and 2015, the Company expensed $0.4 million, $1.0 million and $1.2 million for services performed by Vantia Limited. As of April 30, 2016, the Company had recorded $127,000 within current liabilities for amounts due to Vantia Limited. Following the Carbylan transaction Vantia Limited ceased being a related party.

Carbylan Transaction

12 Months Ended

Apr. 30, 2017

Business Combinations [Abstract]

Carbylan Transaction

Note 6. Carbylan Transaction

On November 21, 2016, KalVista Pharmaceuticals Limited (“KalVista Limited”) completed a share purchase transaction with Carbylan Therapeutics Inc. (“Carbylan”) whereby immediately following the transaction Carbylan’s equity holders owned 19% and KalVista Limited’s equity holders owned 81% of the combined company, respectively. As a result, Carbylan issued approximately 7.8 million shares of common stock to the stockholders of KalVista Limited in exchange for all shares of KalVista Limited. Approximately 1.9 million shares were retained by the Carbylan stockholders. The combined company was renamed KalVista Pharmaceuticals, Inc. following the transaction. For accounting purposes, KalVista Limited is considered to be acquiring Carbylan in the transaction, which was determined based upon the terms of the share purchase agreement and other factors including: (i) KalVista Limited security holders own approximately 81% of the voting interests of the combined company immediately following the closing of the transaction; (ii) directors appointed by KalVista Limited hold a majority of board seats in the combined company; and (iii) KalVista Limited management hold all of the key positions in the management of the combined company. As the accounting acquirer, KalVista Limited’s assets and liabilities were recorded at their pre-combination carrying amounts and the historical operations that are reflected in the financial statements are those of KalVista Limited. The Company incurred $5.6 million of nonrecurring expenses for the year ended April 30, 2017, related to severance, legal and other professional services in connection with the transaction.

The Company’s consolidated financial statements reflect Carbylan’s results of operations beginning after November 21, 2016. The results of operations subsequent to November 21, 2016 have not been significant.

KalVista has concluded that the transaction represents a business combination. Under the acquisition method of accounting, the total purchase price is allocated to the acquired tangible and intangible assets and assumed liabilities of Carbylan based on estimated fair values as of the transaction closing date. Carbylan had no significant commercial operations and its only significant pre-combination net assets were cash and cash equivalents, accounts payable and accrued expenses which were already recognized at fair value. The Company is still evaluating the potential use or disposition of the Carbylan intellectual property. Pursuant to this reverse acquisition, the Company recorded the shares of common stock held by Carbylan shareholders at the fair value of Carbylan’s net monetary assets received at November 21, 2016 as these values were considered a more reliable indicator of fair value than the trading value of the shares. No goodwill or intangible assets were recorded in the transaction.

The preliminary allocation of the total purchase price to the acquired assets and liabilities assumed of Carbylan based on the fair values as of November 21, 2016 is as follows (in thousands):

Cash and cash equivalents	$	34,139
Prepaid expenses and other current assets		70
Accounts payable, accrued expenses and other liabilities		(3,631	)
Net assets acquired	$	30,578

In connection with the share purchase transaction, the Company replaced the options previously granted to purchase shares of KalVista Limited with options to purchase shares of KalVista Pharmaceuticals, Inc. The Company assessed the replacement awards and determined there was no compensation expense to record related to the modification.

Stockholders’ Equity	12 Months Ended
Stockholders’ Equity	Apr. 30, 2017
Equity [Abstract]
Stockholders’ Equity	Note 7. Stockholders’ Equity Prior to the Carbylan transaction, the Company had three classes of shares: Series B Convertible Preferred, Series A Convertible Preferred, and Ordinary, all of which had a par value of $0.0016. Per the terms of the Share Purchase Agreement, the three classes of stock were converted into common shares with a par value of $0.001. In March 2017, the Company established the 2017 Employee Stock Purchase Plan. There are 100,000 shares of common stock available for issuance under the plan.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Grant Income	12 Months Ended
Grant Income	Apr. 30, 2017
Revenues [Abstract]
Grant Income	Note 8. Grant Income Grant income is recognized through two agreements. The first agreement is with the Technology Strategy Board (TSB), a United Kingdom government organization. The Company recognizes revenue for reimbursements of qualifying research and development costs as the services are performed. The Company records these reimbursements as revenue and not as a reduction of research and development expenses, as the Company has the risks and rewards as the principal in the research and development activities. Any services performed and not yet collected upon are shown as a receivable. During the years ended April 30, 2017, 2016 and 2015, revenue recognized through the TSB grant amounted to $1.2 million, $1.8 million and $1.5 million, respectively. The TSB has authorized a total amount of $7.3 million over the lifetime of the agreements between us and the TSB, to accelerate the development of the oral drug program, of which $5.9 million was received or was due to be received as of April 30, 2017. The second agreement is with the JDRF, a non-profit organization. The Company applies the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgement from the grantor and other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either the Company’s performance or on the occurrence of a specific outcome resulting from the Company’s performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to the Company. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement. The Company assesses whether a milestone is substantive at the inception of the arrangement. If a milestone is deemed non-substantive, the Company accounts for that milestone payment in accordance with the multiple element arrangements guidance and recognizes revenue consistent with the related units of accounting for the arrangement over the related performance period. The Company had a contract in process with JDRF that was accounted for under the milestone method. Milestones included, for example, the successful completions of clinical trials, development of certain reports, and different review/approval processes. All milestones under the contract in process were deemed substantive based on the fact that the payments are commensurate with the Company’s efforts to achieve the milestone event and the milestones are related to past performance and are non-refundable. During the years ended April 30, 2017, 2016 and 2015, revenue recognized through the achievement of multiple milestones amounted to $0.2 million, $0.3 million and $0.3 million, respectively. The last milestone in the JDRF contract was met in May 2016 and no additional revenue is due from this contract. There are no performance, cancellation, termination or refund provisions in the arrangement that contain material financial consequences to the Company. The Company evaluates the terms of sponsored research agreement grants and federal grants to assess the Company’s obligations and if the Company’s obligations are satisfied by the passage of time, revenue is recognized as described above. For grants with refund provisions, the Company reviews the grant to determine the likelihood of repayment. If the likelihood of repayment of the grant is determined to be remote, the grant is recognized as revenue. If the probability of repayment is determined to be more than remote, the Company records the grant as a deferred revenue liability, until such time that the grant requirements have been satisfied.

Stock-Based Compensation

12 Months Ended

Apr. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 9. Stock-Based Compensation

The Company has three plans that provide for equity-based compensation. There are two legacy plan that were maintained by Carbylan and KalVista Limited and for which no further grants are to be made. Under the 2017 Equity Incentive Plan, 1,000,000 shares of KalVista’s Common Stock are reserved for issuance upon exercise of stock options. During the year ended April 30, 2017, 85,055 stock options were granted outside of equity incentive plans as inducement stock options to new employees.

New hire grants 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:

	2017	2016	2015
Risk-free interest rate	2.08%	1.38%	1.84%
Expected life of the options	6.25 years	6.25 years	6.25 years
Expected volatility of the underlying stock	82.3%	80.9%	85.1%
Expected dividend rate	0%	0%	0%

For the years ended April 30, 2017, 2016 and 2015, the Company recognized share-based compensation expense of $394,000, $118,000 and $36,000, respectively. Stock-based compensation was reflected in the Company’s consolidated statement of operations and comprehensive loss as follows (in thousands):

	Year ended April 30,
	2017		2016		2015
Research and development	$	143	$	118	$	36
General and administrative		251		—		—
Total stock-based compensation expense	$	394	$	118	$	36

A summary of option activity for the year endeed April 30, 2017 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, 2016		855,790		$	0.004		8.68	$	—
Exercised		(126,948	)		.003
Effect of Carbylan transaction		(516,680	)
Granted		326,203			7.94
Cancelled		(597	)		.004
Outstanding at April 30, 2017		537,768		$	4.82		9.05	$	1,631
Exercisable at April 30, 2017		148,469		$	1.66		7.88	$	890
Vested and expected to vest at April 30, 2017		537,768		$	4.82		9.05	$	1,631

The weighted-average grant date fair value of stock options granted during the years ended April 30, 2017, 2016 and 2015 was $5.68, $1.41 and $1.44, respectively.

As of April 30, 2017, there was $1.6 million of unrecognized compensation expense related to unvested awards, which is expected to be recognized over a weighted-average period of 2.94 years

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Commitments and Contingencies

12 Months Ended

Apr. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 10. Commitments and Contingencies

Lease commitments: The Company is party to several operating leases for office and laboratory space as well as certain lab equipment. Rent expense was $0.5 million, $0.1 million and $0.1 million for the years ended April 30, 2017, 2016 and 2015, respectively, and is reflected in general and administrative expenses and research and development expenses as determined by the underlying activities.

Future minimum payments under these leases as of April 30, 2017 are as follows (in thousands):

Year ended April 30:
2018	$	506
2019		435
2020		261
2021		228
2022 and thereafter		328
Total	$	1,758

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 have been no contingent liabilities requiring accrual at April 30, 2017 and 2016.

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 or timing of any such liability.

Income Taxes

12 Months Ended

Apr. 30, 2017

Income Tax Disclosure [Abstract]

Income Taxes

Note 11. Income Taxes

The Company has incurred net losses since inception and, consequently, has not recorded any U.S. Federal and state income tax expense or benefit for the years presented. In 2017, $2.1 million of the Company’s pre-tax loss was domestic and $16.5 million was foreign. The pre-tax losses in fiscal years 2016 and 2015 were all from the Company’s U.K. operations. The Company files tax returns in the United Kingdom as well as U.S. Federal and various State tax returns. Tax years 2017 and 2016 in the U.K. subsidiary remain open to examination by the Her Majesty’s Revenue and Customs (“HMRC”). Further, HMRC will be able to open an inquiry under the ‘discovery assessment’ for the 2014 tax year until April 30, 2018 if HMRC discovers facts which were not disclosed or readily inferable from the tax returns or accounts. The U.S. returns are open for all tax years since inception. The Company is not currently under examination in any jurisdiction for any tax years.

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

	2017			2016			2015
Income tax benefit at U.S. federal statutory rate		34.00	%		34.00	%		34.00	%
Foreign rate differential		(11.72	)%		(14.00	)%		(13.08	)%
Nondeductible expenses		(9.16	)%		(6.85	)%		(5.24	)%
Other		(1.29	)%		—			—
Valuation allowance		(11.83	)%		(13.15	)%		(15.68	)%
		0.00	%		0.00	%		0.00	%

The Company has net operating loss carry forwards available to offset future taxable income for federal and state income tax purposes. 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 an ownership change occurred as a result of the Company’s transaction in November 2016. As a result of this ownership change, the Company’s U.S. federal and California NOL’s may be limited to the extent of recognizing any previously unrecognized built-in gains of Carbylan as of November 2016.

The tax effect of significant temporary differences representing deferred tax assets and liabilities as of April 30, 2017 and 2016 is as follows (in thousands):

	2017			2016
Net operating loss (“NOL”) carryforwards	$	5,602		$	2,756
Other		282			90
Valuation allowance		(5,884	)		(2,846	)
Net deferred tax asset	$	—		$	—

Management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of NOL carryforwards. As a result of the fact that the Company has incurred tax losses from inception, management has determined that it is more likely than not that the Company will not recognize the benefits of net deferred tax assets and, as a result, a full valuation allowance has been established against its net deferred tax assets as of April 30, 2017 and 2016. During the years ended April 30, 2017, 2016 and 2015, the valuation allowance changed by $3.0 million, $0.4 million and $0.5 million, respectively. Realization of deferred tax assets is dependent upon the generation of future taxable income. As of April 30, 2017, the Company had NOL carryforwards for federal income tax purposes of approximately $1.3 million that begin to expire in 2024 through 2037, NOL carryforwards for state income taxes of $1.3 million that begin to expire in 2026 through 2037 and NOL carryforwards for U.K. income taxes of $26.7 million that do not expire.

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 has no unrecognized tax benefits as of April 30, 2017 and April 30, 2016, respectively. The Company does not expect any material changes in the next 12 months in unrecognized tax benefits. The Company has not recognized interest and penalties related to uncertain tax positions.

Defined Contribution Plans	12 Months Ended
Defined Contribution Plans	Apr. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plans	Note 12. 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. Full-time employees of the U.S. parent company are eligible to participate in the Company's 401(k) Plan. The Company will match up to 4% of employee contributions to the Plan. Total employer contributions to both plans for the years ended April 30, 2017, 2016 and 2015 were $90,000, $70,000 and $66,000 respectively.

Other Income	12 Months Ended
Other Income	Apr. 30, 2017
Other Nonoperating Income Expense [Abstract]
Other Income	Note 13. Other Income As of April 30, 2017 and 2016, the Company had research and development tax credits totaling $2.2 million and $1.9 million, respectively. This tax credit is related to a tax scheme for small and medium enterprises in the United Kingdom as well as the R&D expenditure credit system. The Company is able to file a claim for cash credit in proportion to the Company’s R&D expenditure for the year. This amount was 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 $2.3 million, $2.0 million and $0.8 million related to these programs in the years ended April 30, 2017, 2016 and 2015, respectively.

Subsequent Events	12 Months Ended
Subsequent Events	Apr. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	Note 14. Subsequent Events In May 2017, the Company entered into a lease for approximately 2,700 square feet of office space in Cambridge, MA, that the Company anticipates to occupy in late 2017. The lease has a term of 5 years and annual rent expense will range from approximately $220,000 to $232,000. In June 2017, the Company entered into a lease agreement for laboratory equipment to be used in the U.K. research facility. This lease requires a prepayment of approximately $200,000 and the remaining payments of approximately $18,000 per month will be made over a two year term.

Unaudited Quarterly Financial Information

12 Months Ended

Apr. 30, 2017

Quarterly Financial Information Disclosure [Abstract]

Unaudited Quarterly Financial Information

Note 15. Unaudited Quarterly Financial Information (in thousands):

	Quarter ended July 31, 2016			Quarter ended October 31, 2016			Quarter ended January 31, 2017			Quarter ended April 30, 2017
Grant income	$	975		$	197		$	248		$	114
Operating expenses		6,095			4,223			8,365			5,200
Net loss		(3,436	)		(3,297	)		(7,644	)		(4,202	)
Net loss per share	$	(6.66	)	$	(5.98	)	$	(1.03	)	$	(0.43	)

	Quarter ended July 31, 2015			Quarter ended October 31, 2015			Quarter ended January 31, 2016			Quarter ended April 30, 2016
Grant income	$	839		$	667		$	348		$	314
Operating expenses		3,302			4,192			4,163			5,400
Net loss		(1,716	)		(2,599	)		(1,952	)		(4,869	)
Net loss per share	$	(5.23	)	$	(5.95	)	$	(4.85	)	$	(9.37	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Apr. 30, 2017

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 Attributable to Common Shareholders

Potential dilutive common share equivalents consist of:

	April 30,
	2017		2016		2015
Preferred stock		—		24,322,898		24,322,898
Stock options		148,469		76,643		62,424

Basic and diluted net loss per share	April 30,
	2017			2016			2015
Net loss	$	(18,603	)	$	(11,436	)	$	(7,226	)
Less: dividend on Series A		(935	)		(1,918	)		(1,977	)
Less: dividend on Series B		(1,237	)		(2,121	)		—
Loss available to common stockholders		(20,775	)		(15,475	)		(9,203	)
Weighted average common shares, basic and diluted		4,646,764			591,298			263,358
Net loss per share, basic and diluted	$	(4.47	)	$	(26.17	)	$	(34.94	)

Fair Value Measurement

Correction

Recently Issued Accounting Pronouncements

Recently adopted accounting pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Apr. 30, 2017

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,
	2017		2016		2015
Preferred stock		—		24,322,898		24,322,898
Stock options		148,469		76,643		62,424

Schedule of Basic and Diluted Net Loss Per Share

Basic and diluted net loss per share	April 30,
	2017			2016			2015
Net loss	$	(18,603	)	$	(11,436	)	$	(7,226	)
Less: dividend on Series A		(935	)		(1,918	)		(1,977	)
Less: dividend on Series B		(1,237	)		(2,121	)		—
Loss available to common stockholders		(20,775	)		(15,475	)		(9,203	)
Weighted average common shares, basic and diluted		4,646,764			591,298			263,358
Net loss per share, basic and diluted	$	(4.47	)	$	(26.17	)	$	(34.94	)

Property and Equipment (Tables)

12 Months Ended

Apr. 30, 2017

Property Plant And Equipment [Abstract]

Components of Property and Equipment

At April 30, 2017 and 2016, property and equipment consisted of (in thousands):

	2017			2016
Laboratory equipment	$	373		$	358
Office equipment		31			58
Furniture & Fixtures		6			2
		410			418
Less accumulated depreciation		(313	)		(344	)
	$	97		$	74

Accrued Expenses (Tables)

12 Months Ended

Apr. 30, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

At April 30, 2017 and 2016, accrued expenses consisted of (in thousands):

	2017		2016
Accrued research expense	$	348	$	1,059
Accrued compensation		1,300		966
Accrued professional fees		146		60
Other accrued expenses		71		29
	$	1,865	$	2,114

Carbylan Transaction (Tables)

12 Months Ended

Apr. 30, 2017

Business Combinations [Abstract]

Schedule of Preliminary Allocation of Total Purchase Price to Acquired Assets and Liabilities Assumed

The preliminary allocation of the total purchase price to the acquired assets and liabilities assumed of Carbylan based on the fair values as of November 21, 2016 is as follows (in thousands):

Cash and cash equivalents	$	34,139
Prepaid expenses and other current assets		70
Accounts payable, accrued expenses and other liabilities		(3,631	)
Net assets acquired	$	30,578

Stock-Based Compensation (Tables)

12 Months Ended

Apr. 30, 2017

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:

	2017	2016	2015
Risk-free interest rate	2.08%	1.38%	1.84%
Expected life of the options	6.25 years	6.25 years	6.25 years
Expected volatility of the underlying stock	82.3%	80.9%	85.1%
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,
	2017		2016		2015
Research and development	$	143	$	118	$	36
General and administrative		251		—		—
Total stock-based compensation expense	$	394	$	118	$	36

Summary of Option Activity

A summary of option activity for the year endeed April 30, 2017 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, 2016		855,790		$	0.004		8.68	$	—
Exercised		(126,948	)		.003
Effect of Carbylan transaction		(516,680	)
Granted		326,203			7.94
Cancelled		(597	)		.004
Outstanding at April 30, 2017		537,768		$	4.82		9.05	$	1,631
Exercisable at April 30, 2017		148,469		$	1.66		7.88	$	890
Vested and expected to vest at April 30, 2017		537,768		$	4.82		9.05	$	1,631

Commitments and Contingencies (Tables)

12 Months Ended

Apr. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Under Operating Leases

Future minimum payments under these leases as of April 30, 2017 are as follows (in thousands):

Year ended April 30:
2018	$	506
2019		435
2020		261
2021		228
2022 and thereafter		328
Total	$	1,758

Income Taxes (Tables)

12 Months Ended

Apr. 30, 2017

Income Tax Disclosure [Abstract]

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:

	2017			2016			2015
Income tax benefit at U.S. federal statutory rate		34.00	%		34.00	%		34.00	%
Foreign rate differential		(11.72	)%		(14.00	)%		(13.08	)%
Nondeductible expenses		(9.16	)%		(6.85	)%		(5.24	)%
Other		(1.29	)%		—			—
Valuation allowance		(11.83	)%		(13.15	)%		(15.68	)%
		0.00	%		0.00	%		0.00	%

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, 2017 and 2016 is as follows (in thousands):

	2017			2016
Net operating loss (“NOL”) carryforwards	$	5,602		$	2,756
Other		282			90
Valuation allowance		(5,884	)		(2,846	)
Net deferred tax asset	$	—		$	—

Unaudited Quarterly Financial Information (Tables)

12 Months Ended

Apr. 30, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary of Unaudited Quarterly Financial Information

	Quarter ended July 31, 2016			Quarter ended October 31, 2016			Quarter ended January 31, 2017			Quarter ended April 30, 2017
Grant income	$	975		$	197		$	248		$	114
Operating expenses		6,095			4,223			8,365			5,200
Net loss		(3,436	)		(3,297	)		(7,644	)		(4,202	)
Net loss per share	$	(6.66	)	$	(5.98	)	$	(1.03	)	$	(0.43	)

	Quarter ended July 31, 2015			Quarter ended October 31, 2015			Quarter ended January 31, 2016			Quarter ended April 30, 2016
Grant income	$	839		$	667		$	348		$	314
Operating expenses		3,302			4,192			4,163			5,400
Net loss		(1,716	)		(2,599	)		(1,952	)		(4,869	)
Net loss per share	$	(5.23	)	$	(5.95	)	$	(4.85	)	$	(9.37	)

Description of Business, Basis of Presentation and Going Concern - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions		12 Months Ended
	Nov. 21, 2016	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Organization And Basis Of Presentation [Line Items]
Percentage of voting interest owned	81.00%
Accumulated deficit		$ 55,855	$ 37,252
Cash and cash equivalents		$ 30,950	$ 21,764	$ 2,526	$ 481
Carbylan Therapeutics Inc. [Member]
Organization And Basis Of Presentation [Line Items]
Date of share purchase transaction		Nov. 21, 2016
Percentage of interest owned by equity holders	19.00%
Common shares issued to stockholders	7.8
Common shares retained by stockholders	1.9

Summary of Significant Accounting Policies - Estimated Useful Life of Property and Equipment (Detail)	12 Months Ended
	Apr. 30, 2017
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, 2017	Apr. 30, 2016	Apr. 30, 2015
Summary of Significant Accounting Policies [Line Items]
Uncertain tax positions	$ 0	$ 0	$ 0
Interest or penalties charges recognized	0	0	0
Undistributed loss allocated to holders of convertible preferred shares	0
Total comprehensive loss	$ (21,171,000)	(13,676,000)	(7,382,000)
Previously Reported [Member] \| Restated to Correct Errors in Foreign Currency Translation Adjustments [Member]
Summary of Significant Accounting Policies [Line Items]
Total comprehensive loss		$ (9,196,000)	$ (7,070,000)

Summary of Significant Accounting Policies - Schedule of Potential Dilutive Common Share Equivalents (Detail) - shares	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive potential common share equivalents outstanding		24,322,898	24,322,898
Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive potential common share equivalents outstanding	148,469	76,643	62,424

Summary of Significant Accounting Policies - Schedule of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Earnings Per Share Basic [Line Items]
Net loss	$ (4,202)	$ (7,644)	$ (3,297)	$ (3,436)	$ (4,869)	$ (1,952)	$ (2,599)	$ (1,716)	$ (18,603)	$ (11,436)	$ (7,226)
Loss available to common stockholders									$ (20,775)	$ (15,475)	$ (9,203)
Weighted average common shares, basic and diluted									4,646,764	591,298	263,358
Net loss per share, basic and diluted	$ (0.43)	$ (1.03)	$ (5.98)	$ (6.66)	$ (9.37)	$ (4.85)	$ (5.95)	$ (5.23)	$ (4.47)	$ (26.17)	$ (34.94)
Series A Preferred Shares [Member]
Earnings Per Share Basic [Line Items]
Less: dividend									$ (935)	$ (1,918)	$ (1,977)
Series B Preferred Shares [Member]
Earnings Per Share Basic [Line Items]
Less: dividend									$ (1,237)	$ (2,121)

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 410	$ 418
Less accumulated depreciation	(313)	(344)
Total property and equipment, net	97	74
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	373	358
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	31	58
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 6	$ 2

Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Property Plant And Equipment [Abstract]
Depreciation expense	$ 40,000	$ 33,000	$ 38,000

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Payables And Accruals [Abstract]
Accrued research expense	$ 348	$ 1,059
Accrued compensation	1,300	966
Accrued professional fees	146	60
Other accrued expenses	71	29
Total accrued expenses	$ 1,865	$ 2,114

Related Party Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015	May 23, 2011
Related Party Transaction [Line Items]
Amount recorded within current liabilities		$ 127
Series A Convertible Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares issued for consideration	0	15,900,000
Subscription price per share	$ 0.0016	$ 0.0016
Vantia Limited [Member]
Related Party Transaction [Line Items]
Agreement commencement date	May 23, 2011
Expenses incurred for services performed	$ 400	$ 1,000	$ 1,200
Amount recorded within current liabilities		$ 127,000
Sale and Purchase Agreement [Member] \| Vantia Limited [Member]
Related Party Transaction [Line Items]
Agreement commencement date	May 23, 2011
Sale and Purchase Agreement [Member] \| Vantia Limited [Member] \| Series A Convertible Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares issued for consideration				500,000
Subscription price per share				$ 1.61

Carbylan Transaction - Additional Information (Detail) - USD ($) shares in Millions		12 Months Ended
	Nov. 21, 2016	Apr. 30, 2017
Business Acquisition [Line Items]
Percentage of voting interest owned	81.00%
Nonrecurring expenses related to severance, legal and other professional services		$ 5,600,000
Compensation expense related to modification	$ 0
Carbylan Therapeutics Inc. [Member]
Business Acquisition [Line Items]
Percentage of interest owned by equity holders	19.00%
Common shares issued to stockholders	7.8
Common shares retained by stockholders	1.9
Date of share purchase transaction		Nov. 21, 2016
Goodwill	$ 0
Intangible assets	$ 0

Carbylan Transaction - Schedule of Preliminary Allocation of Total Purchase Price to Acquired Assets and Liabilities Assumed (Detail) - Carbylan Therapeutics Inc. [Member] $ in Thousands	Nov. 21, 2016 USD ($)
Business Acquisition [Line Items]
Cash and cash equivalents	$ 34,139
Prepaid expenses and other current assets	70
Accounts payable, accrued expenses and other liabilities	(3,631)
Net assets acquired	$ 30,578

Stockholders' Equity - Additional Information (Detail) - $ / shares	Apr. 30, 2017	Apr. 30, 2016
Class Of Stock [Line Items]
Ordinary shares, par value	$ 0.0016	$ 0.0016
Common stock, par value	$ 0.001	$ 0.001
2017 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock available for issuance	100,000
Series B Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred shares, par value	$ 0.0016
Series A Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred shares, par value	$ 0.0016

Grant Income - Additional Information (Detail)	1 Months Ended	3 Months Ended								12 Months Ended
Grant Income - Additional Information (Detail)	May 31, 2016 USD ($)	Apr. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)	Oct. 31, 2015 USD ($)	Jul. 31, 2015 USD ($)	Apr. 30, 2017 USD ($) Agreement	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Number of grant income agreements \| Agreement										2
Revenue recognized		$ 114,000	$ 248,000	$ 197,000	$ 975,000	$ 314,000	$ 348,000	$ 667,000	$ 839,000	$ 1,504,000	$ 2,133,000	$ 1,804,000
Grant income received or due to be received under agreement		297,000				$ 356,000				297,000	356,000
Technology Strategy Board (TSB) [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue recognized										1,200,000	1,800,000	1,500,000
Total amount over lifetime of agreement		7,300,000								7,300,000
Grant income received or due to be received under agreement		$ 5,900,000								5,900,000
JDRF [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue recognized through achievement of multiple milestones	$ 0									$ 200,000	$ 300,000	$ 300,000

Stock-Based Compensation - Additional Information (Detail)	12 Months Ended
	Apr. 30, 2017 USD ($) Plan $ / shares shares	Apr. 30, 2016 USD ($) $ / shares	Apr. 30, 2015 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
Stock options, granted	326,203
Share-based compensation expense \| $	$ 394,000	$ 118,000	$ 36,000
Weighted-average grant date fair value of stock options granted \| $ / shares	$ 5.68	$ 1.41	$ 1.44
Unrecognized compensation expense related to unvested awards \| $	$ 1,600,000
Unrecognized compensation expense related to unvested awards expected to be recognized over a weighted-average period	2 years 11 months 9 days
2017 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance upon exercise of stock options	1,000,000
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, granted	85,055
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

Stock-Based Compensation - Schedule of Fair Value of Share-based Awards Measured with Weighted-Average Assumptions (Detail)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.08%	1.38%	1.84%
Expected life of the options	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility of the underlying stock	82.30%	80.90%	85.10%
Expected dividend rate	0.00%	0.00%	0.00%

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	$ 394,000	$ 118,000	$ 36,000
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	143,000	$ 118,000	$ 36,000
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	$ 251,000

Stock-Based Compensation - Summary of Option Activity (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding Beginning Balance	855,790
Shares, Exercised	(126,948)
Effect of Carbylan transaction	(516,680)
Shares, Granted	326,203
Shares, Cancelled	(597)
Shares, Outstanding Ending Balance	537,768	855,790
Shares, Exercisable	148,469
Shares, Vested and expected to vest	537,768
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 0.004
Weighted Average Exercise Price, Exercised	0.003
Weighted Average Exercise Price, Granted	7.94
Weighted Average Exercise Price, Cancelled	0.004
Weighted Average Exercise Price, Outstanding Ending Balance	4.82	$ 0.004
Weighted Average Exercise Price, Exercisable	1.66
Weighted Average Exercise Price, Vested and expected to vest	$ 4.82
Weighted Average Remaining Contractual Life, Outstanding	9 years 18 days	8 years 8 months 5 days
Weighted Average Remaining Contractual Life, Exercisable	7 years 10 months 17 days
Weighted Average Remaining Contractual Life, Vested and expected to vest	9 years 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance	$ 1,631
Aggregate Intrinsic Value, Exercisable	890
Aggregate Intrinsic Value, Vested and expected to vest	$ 1,631

Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)	Apr. 30, 2017 GBP (£)
Other Commitments [Line Items]
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
General and Administrative Expenses and Research and Development Expenses [Member]
Other Commitments [Line Items]
Rent expense	$ 500,000	$ 100,000	$ 100,000

Commitments and Contingencies - Schedule of Future Minimum Payments Under Operating Leases (Detail) $ in Thousands	Apr. 30, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 506
2019	435
2020	261
2021	228
2022 and thereafter	328
Total	$ 1,758

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ 0	$ 0	$ 0
Pre-tax loss from domestic	2,100,000
Pre-tax loss from foreign	$ 16,500,000
Description of income tax examination	Tax years 2017 and 2016 in the U.K. subsidiary remain open to examination by the Her Majesty’s Revenue and Customs (“HMRC”). Further, HMRC will be able to open an inquiry under the ‘discovery assessment’ for the 2014 tax year until April 30, 2018 if HMRC discovers facts which were not disclosed or readily inferable from the tax returns or accounts. The U.S. returns are open for all tax years since inception. The Company is not currently under examination in any jurisdiction for any tax years.
Change in valuation allowance	$ 3,000,000	400,000	500,000
Unrecognized tax benefits	0	0	0
Material changes in the next twelve months in unrecognized tax benefits	0
Interest and penalties related to uncertain tax positions	0	$ 0	$ 0
Federal Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 1,300,000
Federal Income Tax [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2024
Federal Income Tax [Member] \| Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2037
State Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 1,300,000
State Income Tax [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2026
State Income Tax [Member] \| Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration period	2037
U.K. Income Tax [Member]
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 26,700,000

Income Taxes - Schedule of Reconciliation between Effective Tax Rates and Statutory Rates (Detail)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Income tax benefit at U.S. federal statutory rate	34.00%	34.00%	34.00%
Foreign rate differential	(11.72%)	(14.00%)	(13.08%)
Nondeductible expenses	(9.16%)	(6.85%)	(5.24%)
Other	(1.29%)
Valuation allowance	(11.83%)	(13.15%)	(15.68%)
Effective income tax rate	0.00%	0.00%	0.00%

Income Taxes - Schedule of Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Income Tax Disclosure [Abstract]
Net operating loss (“NOL”) carryforwards	$ 5,602	$ 2,756
Other	282	90
Valuation allowance	$ (5,884)	$ (2,846)

Defined Contribution Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
U.S. Employees 401(K) Plan [Member] \| Maximum [Member]
Defined Benefit 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 Benefit Plan Disclosure [Line Items]
Total employer contributions	$ 90,000	$ 70,000	$ 66,000

Other Income - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Other Nonoperating Income Expense [Line Items]
Other income	$ 2,329	$ 2,034	$ 844
Research and Development Tax Credits [Member]
Other Nonoperating Income Expense [Line Items]
Other income	$ 2,200	$ 1,900

Subsequent Events - Additional Information (Detail) - Subsequent Events [Member]	1 Months Ended
	Jun. 30, 2017 USD ($)	May 31, 2017 USD ($) ft²
Office Space in Cambridge, MA [Member]
Subsequent Event [Line Items]
Area of lease premises \| ft²		2,700
Lease term		5 years
Office Space in Cambridge, MA [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Annual rent expense		$ 220,000
Office Space in Cambridge, MA [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Annual rent expense		$ 232,000
U.K. Research Facility [Member]
Subsequent Event [Line Items]
Lease description	This lease requires a prepayment of approximately $200 and the remaining payments of approximately $18 per month will be made over a two year term.
Lease prepayment amount	$ 200,000
Remaining lease payments payable per month	$ 18,000
Period of remaining lease payments payable per month	2 years

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, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Grant income	$ 114	$ 248	$ 197	$ 975	$ 314	$ 348	$ 667	$ 839	$ 1,504	$ 2,133	$ 1,804
Operating expenses	5,200	8,365	4,223	6,095	5,400	4,163	4,192	3,302	23,843	17,314	9,893
Net loss	$ (4,202)	$ (7,644)	$ (3,297)	$ (3,436)	$ (4,869)	$ (1,952)	$ (2,599)	$ (1,716)	$ (18,603)	$ (11,436)	$ (7,226)
Net loss per share, basic and diluted	$ (0.43)	$ (1.03)	$ (5.98)	$ (6.66)	$ (9.37)	$ (4.85)	$ (5.95)	$ (5.23)	$ (4.47)	$ (26.17)	$ (34.94)