Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019
Cash Flows from Operating Activities
Net loss	$ (22,532)	$ (12,290)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	382	256
Stock-based compensation expense	3,358	2,120
Realized (gain) from available for sale securities	(229)
Amortization of right of use assets	418
Amortization of discount/premium on available for sale securities	136
Foreign currency exchange gain	(224)	(20)
Changes in operating assets and liabilities:
Research and development tax credit receivable	(3,405)	(2,409)
Prepaid expenses and other current assets	(187)	(2,475)
Accounts payable	133	1,748
Accrued expenses	(766)	417
Lease obligations	(416)
Deferred revenue	(8,866)	(13,201)
Net cash used in operating activities	(32,198)	(25,854)
Cash Flows from Investing Activities
Acquisition of property and equipment	(212)	(806)
Purchases of available for sale securities	(45,114)	(55,419)
Sales and maturities of available for sale securities	52,052	850
Net cash provided by (used in) investing activities	6,726	(55,375)
Cash Flows from Financing Activities
Capital lease principal payments	(53)	(155)
Issuance of common stock from equity incentive plans	214	132
Issuance of common stock, net of offering expenses	11,422	87,811
Net cash provided by financing activities	11,583	87,788
Effect of exchange rate changes on cash and cash equivalents	498	(1,269)
Net (decrease) increase in cash and cash equivalents	(13,391)	5,290
Cash and cash equivalents at beginning of period	32,006	51,055
Cash and cash equivalents at end of period	$ 18,615	$ 56,345