Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash Flows from Operating Activities
Net income (loss)	$ 2,494	$ (567)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	6,822	7,724
Non-cash interest expense	3,514	3,320
Deferred income taxes	(4)	115
Share-based compensation expense	3,237	3,646
Changes in operating assets and liabilities:
Accounts receivable and contract assets	(6,811)	(27,846)
Inventories and deferred cost of sales	(10,474)	2,446
Prepaid expenses and other current assets	(336)	(1,480)
Accounts payable and accrued expenses	12,612	14,459
Customer deposits and deferred revenue	1,672	(5,242)
Income taxes receivable and payable, net	172	124
Other, net	(2,413)	905
Net cash provided by (used in) operating activities	10,485	(2,396)
Cash Flows from Investing Activities
Capital expenditures	(1,953)	(1,070)
Proceeds from the sale of investments	55,385	71,130
Payments for purchases of investments	(52,037)	(34,866)
Net cash provided by (used in) investing activities	1,395	35,194
Cash Flows from Financing Activities
Proceeds (net of tax withholdings) from option exercises and employee stock purchase plan	878	956
Restricted stock tax withholdings	(1,625)	(680)
Net cash provided by (used in) financing activities	(747)	276
Effect of exchange rate changes on cash and cash equivalents	(30)	(48)
Net increase (decrease) in cash, cash equivalents, and restricted cash	11,103	33,026
Cash, cash equivalents, and restricted cash - beginning of period	130,283	129,951	$ 129,951
Cash, cash equivalents, and restricted cash - end of period	141,386	162,977	$ 130,283
Supplemental Disclosure of Cash Flow Information
Interest paid	1,803	4,681
Income taxes paid	240	293
Non-cash operating and financing activities
Net transfer of property, plant and equipment to inventory		$ 526
Right-of-use assets obtained in exchange for lease obligations	$ 20,353