Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3044-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Description of Business, Basis of Presentation and Going Concern - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Organization And Basis Of Presentation [Line Items]
Accumulated deficit		$ 71,660	$ 55,855
Cash and cash equivalents		$ 51,055	$ 30,950	$ 21,764	$ 2,526
Option Agreement [Member] \| KalVista Pharmaceuticals Limited [Member] \| Merck Sharp & Dohme Corp. [Member]
Organization And Basis Of Presentation [Line Items]
Agreement commencement month and year		2017-11
Non-refundable upfront fee	$ 37,000