Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Ordinary Shares	Treasury Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Apr. 30, 2019			73,675,083
Beginning balance at Apr. 30, 2019	$ 263,012		$ 754	$ (369)	$ 581,135	$ (1,431)	$ (317,077)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares upon exercise of stock options (in shares)			4,470,226
Issuance of ordinary shares upon exercise of stock options	39,568		$ 51		39,517
Issuance of ordinary shares upon release of restricted stock unit (in shares)			53,424
Issuance of ordinary shares upon release of restricted stock units	1		$ 1
Ordinary shares issued in connection with the acquisition of Endgame (in shares)			1,983,663
Ordinary shares issued in connection with the acquisition of Endgame	167,337		$ 21		167,316
Ordinary shares issued in connection with the acquisition of Endgame held in escrow (in shares)			235,031
Ordinary shares issued in connection with the acquisition of Endgame held in escrow	19,826		$ 2		19,824
Assumption of stock option plan as consideration for acquisition of Endgame	9,309				9,309
Repurchase of unvested RSAs (in shares)			(4,585)
Vesting of ordinary shares subject to repurchase	1,612				1,612
Stock-based compensation	25,284				25,284
Net loss	(91,742)						(91,742)
Foreign currency translation	(1,051)					(1,051)
Ending balance (in shares) at Oct. 31, 2019			80,412,842
Ending balance at Oct. 31, 2019	433,156		$ 829	(369)	843,997	(2,482)	(408,819)
Beginning balance (in shares) at Jul. 31, 2019			76,259,361
Beginning balance at Jul. 31, 2019	255,050		$ 782	(369)	614,532	(1,049)	(358,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares upon exercise of stock options (in shares)			1,936,335
Issuance of ordinary shares upon exercise of stock options	19,456		$ 23		19,433
Issuance of ordinary shares upon release of restricted stock unit (in shares)			3,037
Issuance of ordinary shares upon release of restricted stock units	1		$ 1
Ordinary shares issued in connection with the acquisition of Endgame (in shares)			1,983,663
Ordinary shares issued in connection with the acquisition of Endgame	167,337		$ 21		167,316
Ordinary shares issued in connection with the acquisition of Endgame held in escrow (in shares)			235,031
Ordinary shares issued in connection with the acquisition of Endgame held in escrow	19,826		$ 2		19,824
Assumption of stock option plan as consideration for acquisition of Endgame	9,309				9,309
Repurchase of unvested RSAs (in shares)			(4,585)
Stock-based compensation	13,583				13,583
Net loss	(49,973)						(49,973)
Foreign currency translation	(1,433)					(1,433)
Ending balance (in shares) at Oct. 31, 2019			80,412,842
Ending balance at Oct. 31, 2019	433,156		$ 829	(369)	843,997	(2,482)	(408,819)
Beginning balance (in shares) at Apr. 30, 2020			82,856,978
Beginning balance at Apr. 30, 2020	$ 413,647	$ 367	$ 856	(369)	898,788	(1,377)	(484,251)	$ 367
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Issuance of ordinary shares upon exercise of stock options (in shares)	4,035,115		4,035,115
Issuance of ordinary shares upon exercise of stock options	$ 45,230		$ 47		45,183
Issuance of ordinary shares upon release of restricted stock unit (in shares)			312,898
Issuance of ordinary shares upon release of restricted stock units	0		$ 5		(5)
Stock-based compensation	39,407				39,407
Reclassification of liability-classified awards	2,702				2,702
Net loss	(48,159)		0	0	0	0	(48,159)
Foreign currency translation	(10,537)		$ 0	0	0	(10,537)	0
Ending balance (in shares) at Oct. 31, 2020			87,204,991
Ending balance at Oct. 31, 2020	442,657		$ 908	(369)	986,075	(11,914)	(532,043)
Beginning balance (in shares) at Jul. 31, 2020			85,737,645
Beginning balance at Jul. 31, 2020	432,379		$ 890	(369)	946,178	(11,435)	(502,885)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares upon exercise of stock options (in shares)			1,379,823
Issuance of ordinary shares upon exercise of stock options	15,978		$ 16		15,962
Issuance of ordinary shares upon release of restricted stock unit (in shares)			87,523
Issuance of ordinary shares upon release of restricted stock units	0		$ 2		(2)
Stock-based compensation	21,235				21,235
Reclassification of liability-classified awards	2,702				2,702
Net loss	(29,158)						(29,158)
Foreign currency translation	(479)					(479)
Ending balance (in shares) at Oct. 31, 2020			87,204,991
Ending balance at Oct. 31, 2020	$ 442,657		$ 908	$ (369)	$ 986,075	$ (11,914)	$ (532,043)