CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 11,212	$ (10,466)	$ (4,215)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	3,453	3,091	2,746
Stock-based compensation	3,854	2,499	1,595
Amortization of debt discount and issuance costs	916	0	0
Loss on disposal of assets	0	13	127
Gain on sale of research and development assets	0	0	(1,000)
Changes in operating assets and liabilities:
Accounts receivable	(10,236)	(1,232)	(3,620)
Contract assets	(2,812)	1,027	(1,439)
Inventory	(988)	(4,326)	1,701
Prepaid expenses and other assets	(1,260)	(3)	(28)
Accounts payable	(608)	802	2,125
Accrued payroll and related costs	5,775	(521)	976
Contract liabilities	21,649	14,469	(5,371)
Other accrued expenses and current liabilities	227	474	(642)
Assets and liabilities of discontinued operations	0	0	(4,550)
Net cash provided by (used in) operating activities	31,182	5,827	(11,595)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(9,864)	(3,812)	(1,502)
Proceeds from sale of property and equipment	0	0	46
Proceeds from sale of research and development assets	0	0	6,000
Net cash (used in) provided by investing activities	(9,864)	(3,812)	4,544
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible senior notes, net of issuance costs	138,464	0	0
Purchases of capped calls related to convertible senior notes	(12,837)	0	0
Proceeds from issuance of common stock, net of issuance costs	32,141	0	0
Proceeds from issuance of common stock under equity compensation plans	3,984	1,120	1,536
(Repayment of) proceeds from note payable	(4,379)	4,379	0
Dividends paid on preferred stock	(4,455)	(4,325)	(4,325)
Redemption of preferred stock	(37,051)	0	0
Impact of preferred stock redemption	(3,439)	0	0
Principal payments on finance lease	(93)	(78)	(74)
Net cash provided by (used in) financing activities	112,335	1,096	(2,863)
Net increase (decrease) in cash, cash equivalents and restricted cash	133,653	3,111	(9,914)
Cash, cash equivalents and restricted cash, beginning of period	36,612	33,501	43,415
Cash, cash equivalents and restricted cash, end of period	170,265	36,612	33,501
Supplemental disclosures of cash flow information
Interest paid	5	8	11
Supplemental disclosures of non-cash activities:
Unpaid purchases of property and equipment	3,939	772	318
Decapitalization of right-of-use assets upon lease termination and/or modification	0	1,469	0
Property and equipment acquired under finance lease	$ 0	$ 0	$ 245