Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (5,683)	$ (10,303)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Provision for doubtful accounts	524	490
Depreciation and amortization	10,772	8,277
Loss on disposals of fixed assets	766	488
Compensation expense related to stock-based awards and employee stock purchase plan	3,029	2,459
Unrealized currency translation gain	(35)	(492)
PPP loan forgiveness	(6,979)	0
Changes in operating assets and liabilities:
Accounts receivable	1,194	852
Inventories	34	(1,198)
Prepaid expenses, other current assets, and current contract assets	(955)	(88)
Other non-current assets and non-current contract assets	1,185	(776)
Accounts payable	(2,407)	(3,391)
Contract liabilities and long-term contract liabilities	(739)	(937)
Accrued compensation, product warranty and other	1,206	1,686
Other long-term liabilities	2	5
Net cash provided by (used in) operating activities	1,914	(2,928)
Cash flows from investing activities:
Capital expenditures	(15,239)	(10,206)
Cash paid for acquisition of intangible asset	(47)	(58)
Proceeds from sale of fixed assets	100	6
Purchases of marketable securities	(5)	(6,095)
Maturities and sales of marketable securities	8,000	13,500
Net cash used in investing activities	(7,191)	(2,853)
Cash flows from financing activities:
Proceeds from PPP loan	0	6,927
Proceeds from stock options exercised and employee stock purchase plan	2,846	207
Repurchase of common stock	0	(390)
Payment of finance lease	(228)	(468)
Net cash provided by financing activities	2,618	6,276
Effect of exchange rate changes on cash and cash equivalents	(39)	(711)
Net decrease in cash and cash equivalents	(2,698)	(216)
Cash and cash equivalents at beginning of period	12,578	18,365
Cash and cash equivalents at end of period	9,880	18,149
Supplemental disclosure of non-cash investing activities:
Changes in accrued other and accounts payable related to property and equipment additions	$ 154	$ 265