Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Oct. 31, 2020	Oct. 31, 2019
Cash flows from operating activities
Net loss	$ (21,241)	$ (13,241)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	261	248
Stock-based compensation expense	2,436	2,236
Realized gain from sale of marketable securities	(116)	(129)
Non-cash operating lease expense	17	2
Amortization of premium on marketable securities	137	79
Foreign currency exchange (gain) loss	(168)	(81)
Changes in operating assets and liabilities:
Research and development tax credit receivable	2,322	(577)
Prepaid expenses and other current assets	3,031	785
Accounts payable	446	(558)
Accrued expenses	1,335	(564)
Deferred revenue		(7,289)
Net cash used in operating activities	(11,540)	(19,089)
Cash flows from investing activities
Purchases of marketable securities	(19,342)	(42,561)
Sales and maturities of marketable securities	31,261	39,729
Acquisition of property and equipment	(35)	(212)
Net cash provided by (used in) investing activities	11,884	(3,044)
Cash flows from financing activities
Issuance of common stock, net of offering expenses		11,422
Issuance of common stock from equity incentive plans	106	170
Finance lease principal payments		(54)
Net cash provided by financing activities	106	11,538
Effect of exchange rate changes on cash and cash equivalents	(65)	308
Net increase (decrease) in cash and cash equivalents	385	(10,287)
Cash and cash equivalents at beginning of period	15,789	32,006
Cash and cash equivalents at end of period	$ 16,174	$ 21,719