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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Jan. 31, 2018	Mar. 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jan. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	KALV
Entity Registrant Name	KALVISTA PHARMACEUTICALS, INC.
Entity Central Index Key	0001348911
Current Fiscal Year End Date	--04-30
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		10,795,895

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jan. 31, 2018	Apr. 30, 2017
Current assets:
Cash and cash equivalents	$ 58,678	$ 30,950
Research and development tax credit receivable	4,989	2,250
Grants and other receivables	40	297
Prepaid expenses and other current assets	2,003	701
Total current assets	65,710	34,198
Other assets	173	50
Property and equipment, net	774	97
Total assets	66,657	34,345
Current liabilities:
Accounts payable	1,575	1,153
Accrued expenses	2,290	1,865
Deferred revenue - current portion	19,996
Capital lease liability - current portion	222
Total current liabilities	24,083	3,018
Long-term liabilities:
Deferred revenue - net of current portion	13,889
Capital lease liability - net of current portion	117
Total long-term liabilities	14,006
Commitments and contingencies (Note 4)
Stockholders’ equity
Common stock, $0.001 par value Shares authorized: 100,000,000 Shares issued and outstanding: 10,792,646	11	10
Additional paid-in capital	99,696	89,815
Accumulated deficit	(71,003)	(55,855)
Accumulated other comprehensive loss	(136)	(2,643)
Total stockholders’ equity	28,568	31,327
Total liabilities and stockholders’ equity	$ 66,657	$ 34,345

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Income Statement [Abstract]
Revenue	$ 2,331	$ 248	$ 3,554	$ 1,390
Operating Expenses:
Research and development	4,548	3,339	12,385	9,670
General and administrative	2,129	5,026	6,905	8,973
Total operating expenses	6,677	8,365	19,290	18,643
Operating loss	(4,346)	(8,117)	(15,736)	(17,253)
Other income (expense):
Interest income	14	7	17	31
Foreign currency exchange gain (loss)	(1,887)	(195)	(1,836)	1,511
Other income	985	661	2,407	1,310
Total other income (expense)	(888)	473	588	2,852
Net loss	(5,234)	(7,644)	(15,148)	(14,401)
Other comprehensive loss:
Foreign currency translation adjustments	2,434	166	2,507	(2,832)
Comprehensive loss	$ (2,800)	$ (7,478)	$ (12,641)	$ (17,233)
Net loss per share to common stockholders, basic and diluted	$ (0.49)	$ (1.03)	$ (1.49)	$ (5.50)
Weighted average common shares outstanding, basic and diluted	10,788,556	7,657,874	10,168,520	3,013,073

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Cash Flows from Operating Activities
Net loss	$ (15,148)	$ (14,401)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	129	29
Stock-based compensation	779	228
Foreign currency remeasurement (gain) loss	(500)	(1,464)
Changes in operating assets and liabilities:
Research and development tax credit receivable	(2,383)	(1,303)
Prepaid expenses and other current assets	(1,206)	(689)
Grants and other receivables	281	36
Other assets	(123)
Accounts payable	548	(1,957)
Accrued expenses	332	(1,560)
Deferred revenue	33,804
Net cash provided by (used in) operating activities	16,513	(21,081)
Cash Flows from Investing Activities
Cash acquired in transaction		34,139
Acquisition of property and equipment	(343)	(67)
Net cash provided by (used in) investing activities	(343)	34,072
Cash Flows from Financing Activities
Capital lease principal payments	(101)
Issuance of common stock	9,100	2
Net cash from financing activities	8,999	2
Effect of exchange rate changes on cash	2,559	(1,259)
Net increase in cash and cash equivalents	27,728	11,734
Cash and cash equivalents at beginning of period	30,950	21,764
Cash and cash equivalents at end of period	58,678	33,498
Supplemental Disclosures of Non-cash Financing Activities
Capital leases	$ 513
Conversion of preferred stock to common stock		$ 58,608

The Company

9 Months Ended

Jan. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

The Company

1.	The Company

KalVista Pharmaceuticals, Inc. (“KalVista” or the “Company”) is a clinical stage pharmaceutical company focused on the discovery, development and commercialization of serine protease inhibitors as new treatments for diseases with significant unmet need. The Company’s initial focus is on developing small molecule inhibitors of plasma kallikrein for two indications: hereditary angioedema (“HAE”) and diabetic macular edema (“DME”). The strategy in HAE is to develop a portfolio of program candidates in order to create a best-in-class oral therapy. The Company intends to obtain data on multiple molecules prior to making decisions on which program, or programs, to advance into later stage trials, as well as which specific indications to pursue within HAE.

The Company also has developed KVD001, an intravitreally administered plasma kallikrein inhibitor for DME. In October 2017, the Company’s wholly-owned, U.K. based subsidiary KalVista Pharmaceuticals Limited (“KalVista Limited) and Merck Sharp & Dohme Corp. (“Merck”) entered into an option agreement (the “Option Agreement”) under which the Company granted to Merck an option to acquire KVD001 through a period following completion of a Phase 2 clinical trial. The Company also granted to Merck a similar option to acquire investigational orally delivered molecules for DME (the “Oral DME Compounds”) that it will continue to develop as part of its ongoing research and development activities, through a period following the completion of a Phase 2 clinical trial. Under the terms of the Option Agreement, Merck paid to the Company a non-refundable upfront fee of $37 million in November 2017. See Note 5 for further discussion of the arrangement with Merck.

In January 2018, the Company announced the initiation of a Phase 2 clinical trial for KVD001. This study is anticipated to enroll a total of 123 patients to evaluate the safety and efficacy of KVD001 in patients with DME who have received previous anti-VEGF therapy but continue to demonstrate reduced visual acuity and significant edema. The double-masked study will consist of two active arms receiving low or high dose injections, and a sham control arm. Patients will receive a total of four injections over a three month period, with evaluation at the end of the dosing period and for three months following. The endpoints include safety and tolerability, best corrected visual acuity, central subfield thickness, and the diabetic retinopathy severity scale. The Company anticipates that data from this study will be available in the second half of 2019. Once the Company provides certain data resulting from the study to Merck pursuant to the Option Agreement, Merck will have a defined period to exercise the option on KVD001, as well as to make an additional payment to maintain the option on the Oral DME Compounds.

Also in January 2018, the Company announced the initiation of a first-in-human study for KVD900, the next program to advance to clinical trials from the Company’s HAE portfolio. The Phase 1 trial of KVD900 is dosing healthy volunteers to evaluate the safety, tolerability and exposure of the drug candidate, and a plasma-based assay will be used to assess the pharmacodynamic effect of KVD900. The Company expects to provide an update on the status and progress of the HAE portfolio, including KVD900, in mid-2018. The Company also intends to advance at least one additional HAE drug candidate to the clinic before the end of 2018.

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 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 and sale of preferred stock and common stock, the share purchase transaction with Carbylan Therapeutics, Inc. (“Carbylan”), the Option Agreement, and grant income. As of January 31, 2018, the Company had an accumulated deficit of $71.0 million and $58.7 million of cash and cash equivalents. The Company’s working capital, primarily cash, is anticipated to fund the Company’s operations for at least the next twelve months from the date these interim condensed consolidated financial statements are issued. Accordingly, the unaudited interim condensed consolidated financial statements have been prepared on a going concern basis.

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 Company’s business and prospects.

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

Summary of Significant Accounting Policies

9 Months Ended

Jan. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Principles of Consolidation: The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation.

The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. Such financial statements reflect all adjustments that are, in management’s opinion, necessary to present fairly, in all material respects, the Company’s consolidated financial position, results of operations, and cash flows. There were no adjustments other than normal recurring adjustments. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual financial statements. These unaudited interim condensed consolidated financial results are not necessarily indicative of the results to be expected for the year ending April 30, 2018, or for any other future annual or interim period. The accompanying unaudited interim condensed consolidated financial statements should be read in conjunction with the audited financial statements as of and for the year ended April 30, 2017.

Segment Reporting: The Company’s 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.

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

Potential dilutive common share equivalents consist of:

	January 31,
	2018		2017
Stock Options		315,908		120,127

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 for the periods presented.

Basic and diluted net loss per share (in thousands, except share and per share amounts)	Three Months Ended						Nine Months Ended
	January 31,						January 31,
	2018			2017			2018			2017
Net loss	$	(5,234	)	$	(7,644	)	$	(15,148	)	$	(14,401	)
Less: dividend on Series A		—			91			—			935
Less: dividend on Series B		—			120			—			1,237
Loss available to common shareholders for the purpose of calculating basic and diluted net loss per share	$	(5,234	)	$	(7,855	)	$	(15,148	)	$	(16,573	)
Weighted average common shares, basic and diluted		10,788,556			7,657,874			10,168,520			3,013,073
Net loss per share, basic and diluted	$	(0.49	)	$	(1.03	)	$	(1.49	)	$	(5.50	)

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 reverse merger arising from the share purchase transaction with Carbylan, 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.

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 U.S. GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. 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. The Company’s only significant revenue generating arrangement is the arrangement with Merck, which is currently being evaluated for the impact that the adoption of this 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. See Note 4 for additional information regarding the Company’s lease obligations.

Recently Adopted Accounting Prouncements: In March 2016, the FASB issued ASU No. 2016-09, Compensation –Stock Compensation (Topic 718) (“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. The Company adopted this standard in the quarter ended July 31, 2017, and will account for forfeitures as incurred. The adoption of this standard did not have a material impact on the unaudited interim condensed consolidated financial statements.

Commitments and Contingencies

9 Months Ended

Jan. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

4.	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 duing the course of the toxicology 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 toxicology studies and clinical trials. The remaining commitment, which has cancellation provisions, totals $8.8 million at January 31, 2018.

Lease Commitments: The Company is party to several operating leases for office and laboratory space as well as a capital lease for certain lab equipment, which commenced in the three months ended October 31, 2017. The capital lease has a term of 24 months, for which the Company made a down payment of approximately $102,000 and will make monthly lease payments of approximately $18,000 over the term of the lease. Rent expense is reflected in general and administrative expenses and research and development expenses as determined by the underlying activities.

Future minimum lease payments under these leases as of January 31, 2018 are as follows (in thousands):

Fiscal year	Capital Leases			Operating Leases
2018	$	59		$	86
2019		234			223
2020		59			225
2021		—			228
2022 and thereafter		—			328
Total minimum lease payments		352		$	1,090
Less amounts representing interest		(13	)
Present value of minimum payments		339
Current portion		(222	)
Long-term portion	$	117

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 such expenditures can be reasonably estimated. There are no contingent liabilities requiring accrual at January 31, 2018.

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 $1.0 million within 90 days of the first commercial sale of the product subject to certain limitations, 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.

Merck Arrangement	9 Months Ended
Merck Arrangement	Jan. 31, 2018
License And Collaboration Arrangements [Abstract]
Merck Arrangement	5.Merck Arrangement On October 6, 2017, the Company’s wholly-owned U.K. based subsidiary KalVista Pharmaceuticals Limited (“KalVista Limited) and Merck Sharp & Dohme Corp. (“Merck”) entered into an option agreement (the “Option Agreement”). The Company is the guarantor of KalVista Limited’s obligations under the Option Agreement. Under the terms of the Option Agreement, the Company, through KalVista Limited, has granted to Merck an option to acquire KVD001 through a period following completion of a Phase 2 clinical trial. The Company, through KalVista Limited, has also granted to Merck a similar option to acquire investigational orally delivered molecules for DME that the Company will continue to develop as part of its ongoing research and development activities, 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 is required to use its diligent efforts to develop the two compounds through the completion of Phase 2 clinical trials. The Company will fund and retain control over the planned Phase 2 clinical trial of KVD001 as well as development of the investigational oral DME compounds through Phase 2 clinical trials unless Merck determines to exercise its options earlier, at which point Merck will take responsibility for all development and commercialization activities for the compounds. The Company’s development efforts under the Option Agreement will be 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. If Merck exercises both options under the Option Agreement, KalVista Limited could receive up to an additional $715 million composed of option exercise payments and clinical, regulatory, and sales-based milestone payments. In addition, the Company is eligible for tiered royalties on global net sales ranging from mid-single digits to double digit percentages. Merck may terminate the Option Agreement at any time upon written notice to the Company. KalVista Limited may terminate the Option Agreement in the event of Merck’s material breach of the Option Agreement, subject to cure. Concurrent with the Option Agreement, the Company and Merck also entered into a stock purchase agreement (the “Stock Purchase Agreement”) pursuant to which Merck paid approximately $9.1 million to purchase 1,070,589 new shares of the Company’s common stock at a price of $8.50 per share. The Company determined that the Option Agreement and the Stock Purchase Agreement were negotiated and executed contemporaneously, and therefore should be combined as one arrangement for accounting purposes. The Company evaluated the arrangement in accordance with the provisions of ASC 605-25. The Company determined that the arrangement contains the following deliverables: (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, (iii) research and development services related to the development of the Oral DME Compounds, and (iv) unregistered shares of the Company’s common stock. The Company has determined that Merck’s options to acquire KVD001 and the Oral DME Compounds are substantive options. Merck is not contractually obligated to exercise the options. The Company has determined that Merck’s options to acquire KVD001 and the Oral DME Compounds are not priced at a significant and incremental discount. Consequently, the Company determined that Merck’s options are not deliverables in the arrangement. The Company further determined that the research license granted did not have standalone value 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 on a standalone basis. As a result, the research license has been combined with the respective research and development services for KVD001 and the Oral DME Compounds as two units of accounting (the “KVD001 Unit of Accounting” and the “Oral DME Unit of Accounting”). The Company has concluded that the common stock deliverable identified at the inception of the arrangement has standalone value from the other deliverables and therefore represents a separate unit of accounting (the “Common Stock Unit of Accounting”). Therefore, the Company has identified three units of accounting under the arrangement as follows: (i) the KVD001 Unit of Accounting, (ii) the Oral DME Unit of Accounting, and (iii) the Common Stock Unit of Accounting. Allocable arrangement consideration at inception of the arrangement is comprised of the non-refundable up-front payment of $37.0 million and the payment for the common stock of $9.1 million. The Company allocated the $9.1 million payment to the common stock, as this represented the fair value of the shares issued based on arms-length negotiations between the Company and Merck. The amount allocated to the common stock is recorded to stockholders’ equity at the date of issuance. The Company allocated the remaining allocable consideration of $37.0 million to the remaining units of accounting using the relative-selling price method. The Company determined that neither vendor-specific objective evidence or third-party evidence is available for any of the units of accounting identified at arrangement inception. Accordingly, the selling price of each unit of accounting was developed using management’s best estimate of selling price. The Company developed the Best Estimate of Selling Price (“BESP”) for the KVD001 Unit of Accounting and Oral DME Unit of Accounting by applying a risk-adjusted analysis of discounted cash flows and the allocable arrangement consideration was allocated among the separate units of accounting using the relative selling price method. The amount allocated to each Unit of Accounting will be recognized as revenue on a proportional performance basis. During the three months and nine months ended January 31, 2018, the Company recognized approximately $2.3 million and $3.2 million, respectively, of revenue with respect to the arrangement with Merck. As of January 31, 2018, deferred revenue on the condensed consolidated balance sheet was $33.9 million.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Jan. 31, 2018

Accounting Policies [Abstract]

Principles of Consolidation

Segment Reporting

Net Loss per Share Attributable to Common Shareholders

Potential dilutive common share equivalents consist of:

	January 31,
	2018		2017
Stock Options		315,908		120,127

Basic and diluted net loss per share (in thousands, except share and per share amounts)	Three Months Ended						Nine Months Ended
	January 31,						January 31,
	2018			2017			2018			2017
Net loss	$	(5,234	)	$	(7,644	)	$	(15,148	)	$	(14,401	)
Less: dividend on Series A		—			91			—			935
Less: dividend on Series B		—			120			—			1,237
Loss available to common shareholders for the purpose of calculating basic and diluted net loss per share	$	(5,234	)	$	(7,855	)	$	(15,148	)	$	(16,573	)
Weighted average common shares, basic and diluted		10,788,556			7,657,874			10,168,520			3,013,073
Net loss per share, basic and diluted	$	(0.49	)	$	(1.03	)	$	(1.49	)	$	(5.50	)

Fair Value Measurement

Recently Issued Accounting Pronouncements Adopted and Not Yet Adopted

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Jan. 31, 2018

Accounting Policies [Abstract]

Schedule of Potential Dilutive Common Share Equivalents

Potential dilutive common share equivalents consist of:

	January 31,
	2018		2017
Stock Options		315,908		120,127

Schedule of Basic and Diluted Net Loss Per Share

Basic and diluted net loss per share (in thousands, except share and per share amounts)	Three Months Ended						Nine Months Ended
	January 31,						January 31,
	2018			2017			2018			2017
Net loss	$	(5,234	)	$	(7,644	)	$	(15,148	)	$	(14,401	)
Less: dividend on Series A		—			91			—			935
Less: dividend on Series B		—			120			—			1,237
Loss available to common shareholders for the purpose of calculating basic and diluted net loss per share	$	(5,234	)	$	(7,855	)	$	(15,148	)	$	(16,573	)
Weighted average common shares, basic and diluted		10,788,556			7,657,874			10,168,520			3,013,073
Net loss per share, basic and diluted	$	(0.49	)	$	(1.03	)	$	(1.49	)	$	(5.50	)

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Capital and Operating Leases (Detail) $ in Thousands	Jan. 31, 2018 USD ($)
Capital Leases
2018	$ 59
2019	234
2020	59
Total minimum lease payments	352
Less amounts representing interest	(13)
Present value of minimum payments	339
Current portion	(222)
Long-term portion	117
Operating Leases
2018	86
2019	223
2020	225
2021	228
2022 and thereafter	328
Total minimum lease payments	$ 1,090

Merck Arrangement - Additional Information (Detail)		1 Months Ended	3 Months Ended	9 Months Ended
Merck Arrangement - Additional Information (Detail)	Oct. 06, 2017 USD ($) AccountingUnit $ / shares shares	Nov. 30, 2017 USD ($)	Jan. 31, 2018 USD ($)	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock				$ 9,100,000	$ 2,000
Number of accounting units \| AccountingUnit	3
Research and Development Services for KVD001 and Oral DME [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of accounting units \| AccountingUnit	2
Option Agreement [Member] \| Research and Development Services for KVD001 and Oral DME [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Allocable arrangement consideration for non refundable upfront payment in unit of accounting	$ 37,000,000
Merck Sharp & Dohme Corp. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			$ 2,300,000	3,200,000
Deferred revenue			$ 33,900,000	$ 33,900,000
Merck Sharp & Dohme Corp. [Member] \| Stock Purchase Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock	$ 9,100,000
Number of shares of common stock issued \| shares	1,070,589
Price per share of common stock issued \| $ / shares	$ 8.50
Allocable arrangement consideration for payment to common stock unit of accounting	$ 9,100,000
KalVista Pharmaceuticals Limited [Member] \| Merck Sharp & Dohme Corp. [Member] \| Option Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement commencement date				Oct. 06, 2017
Non-refundable upfront fee		$ 37,000,000
Maximum additional option exercise payments and clinical, regulatory, and sales-based milestone payments could be received if options exercised	$ 715,000,000

Grant Income	9 Months Ended
Grant Income	Jan. 31, 2018
Revenues [Abstract]
Grant Income	6.Grant Income Grant income is primarily recognized through an agreement with the Technology Strategy Board (“TSB”), a United Kingdom government organization. The Company recognizes revenue for reimbursements of research and development costs as the services are performed up to an agreed upon threshold. 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 three and nine months ended January 31 2018 and 2017, revenue recognized through the TSB grant amounted to $6,000 and $248,000, and $0.4 million and $1.4 million, respectively. As of January 31, 2018, the development activities related to the TSB grant have been substantially completed and the Company does not anticipate significant further reimbursements. 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.

Income Taxes	9 Months Ended
Income Taxes	Jan. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	7.Income Taxes The 2017 Tax Act, which was signed into law on December 22, 2017, has resulted in significant changes to the U.S. corporate income tax system. These changes include a federal statutory rate reduction from 35% to 21%, the elimination or reduction of certain domestic deductions and credits, and limitations on the deductibility of interest expense and executive compensation. The 2017 Tax Act also transitions international taxation from a worldwide system to a modified territorial system and includes base erosion prevention measures on non-U.S. earnings, which has the effect of subjecting certain earnings of the Company’s foreign subsidiaries to U.S. taxation as global intangible low-taxed income (“GILTI”), as well as a base erosion and anti-abuse tax (“BEAT”) aimed at preventing the erosion of the U.S. tax base. These changes are effective beginning in the Company’s fiscal year beginning May 1, 2018. The Company’s deferred tax assets and liabilities are measured at the enacted tax rate expected to apply when these temporary differences are expected to be realized or settled. Because of the valuation allowance provided on the Company’s domestic net deferred tax assets, the remeasurement of the deferred tax assets and liabilities to the newly enacted rate has no impact on its tax provision. The 2017 Tax Act eliminates the deferral of U.S. income tax on the historical unrepatriated earnings by imposing the Transition Toll Tax, which is a one-time mandatory deemed repatriation tax on undistributed foreign earnings. The Transition Toll Tax is assessed on the U.S. shareholder's share of the foreign corporation's accumulated foreign earnings that have not previously been taxed. The Company does not have any unrepatriated earnings that are subject to the Transition Toll Tax. The Company’s preliminary conclusion is that GILTI and BEAT likely will not have an impact on its tax provision. However, the Company has not yet concluded on whether the impact of GILTI and BEAT will be included in the measurement of deferred taxes or recognized as assessed as period costs. These preliminary estimates, including the remeasurement of deferred tax assets and liabilities, are subject to the finalization of management’s analysis related to certain matters, such as developing interpretations of the provisions of the 2017 Tax Act, changes to certain estimates, and amounts related to the earnings and profits of foreign subsidiaries that might arise upon filing of the Company’s tax returns. The final determination of the Transition Toll Tax and the remeasurement of deferred assets and liabilities will be completed as additional information becomes available, but not later than one year from the enactment of the 2017 Tax Act.

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Apr. 30, 2017
Payables And Accruals [Abstract]
Accrued compensation expense	$ 1,051	$ 1,300
Accrued research expense	753	348
Accrued professional fees	233	146
Other accrued expenses	253	71
Total accrued expenses	$ 2,290	$ 1,865

Commitments and Contingencies - Additional Information (Detail)	9 Months Ended
	Jan. 31, 2018 USD ($)
Other Commitments [Line Items]
Contractual obligation remaining commitment including cancellation provisions	$ 8,800,000
Capital lease term	24 months
Down payment made for capital lease	$ 102,000
Future monthly payments to be paid over the term of the capital lease	18,000
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

Income Taxes - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Jan. 31, 2018	Apr. 30, 2018
Operating Loss Carryforwards [Line Items]
Federal statutory tax rate	35.00%
Impact on tax provision	$ 0
Scenario Plan [Member]
Operating Loss Carryforwards [Line Items]
Federal statutory tax rate		21.00%

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jan. 31, 2018	Apr. 30, 2017
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	10,792,646	10,792,646
Common stock, shares outstanding	10,792,646	10,792,646

The Company - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Nov. 30, 2017	Jan. 31, 2018	Apr. 30, 2017	Jan. 31, 2017	Apr. 30, 2016
Organization And Basis Of Presentation [Line Items]
Accumulated deficit		$ (71,003)	$ (55,855)
Cash and cash equivalents		$ 58,678	$ 30,950	$ 33,498	$ 21,764
Option Agreement [Member] \| KalVista Pharmaceuticals Limited [Member] \| Merck Sharp & Dohme Corp. [Member]
Organization And Basis Of Presentation [Line Items]
Agreement commencement month and year		2017-10
Non-refundable upfront fee	$ 37,000

Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Jan. 31, 2018 USD ($)
Accounting Policies [Abstract]
Undistributed loss allocated to holders of convertible preferred shares	$ 0

Summary of Significant Accounting Policies - Schedule of Potential Dilutive Common Share Equivalents (Detail) - shares	9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive potential common share equivalents outstanding	315,908	120,127