CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 9,221	$ (5,698)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization	2,540	2,276
Stock-based compensation	2,754	1,849
Loss on lease termination	0	355
Loss on disposal of assets	0	13
Changes in operating assets and liabilities:
Accounts receivable	(18,507)	(2,777)
Contract asssets	(2,245)	(1,784)
Inventory	(1,063)	(3,008)
Prepaid expenses and other assets	(101)	(54)
Accounts payable	(951)	491
Accrued payroll and related costs	3,481	(555)
Contract liabilities	18,587	11,704
Other accrued expenses and liabilities	(394)	(32)
Net cash provided by operating activities	13,322	2,780
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(5,717)	(3,025)
Net cash used in investing activities	(5,717)	(3,025)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs	32,141	0
Proceeds from exercise of stock options	2,179	916
Proceeds from issuance of common stock under employee stock purchase plan	423	187
Repayment of note payable	(4,379)	0
Dividends paid on preferred stock	(3,244)	(3,244)
Principal payments on finance lease	(93)	(78)
Net cash provided by (used in) financing activities	27,027	(2,219)
Net increase (decrease) in cash, cash equivalents and restricted cash	34,632	(2,464)
Cash, cash equivalents and restricted cash, beginning of period	36,612	33,501
Cash, cash equivalents and restricted cash, end of period	71,244	31,037
Supplemental disclosures of cash flow information
Unpaid purchases of property and equipment	1,880	489
Decapitalization of right-of-use assets upon lease termination and/or modification	$ 0	$ 1,469