CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (45,913)	$ (40,539)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,248	1,571
Amortization of investment discount	97	13
Equity-based compensation	15,429	7,615
Amortization of debt discount and issuance costs	6,079	5,426
(Gain) loss on disposal of property and equipment	(100)	527
Contributions to deferred compensation plan	(236)	(160)
(Increase) decrease in assets:
Accounts receivable	(564)	550
Inventory and instruments in property and equipment	(524)	(1,979)
Prepaid expense and other	60	(360)
Increase (decrease) in liabilities:
Accounts payable	564	390
Accrued liabilities, and other	736	(581)
Accrued interest	45	0
Deferred revenue and income	(94)	(39)
Deferred compensation	245	171
Net cash used in operating activities	(22,928)	(27,395)
Cash flows from investing activities:
Purchases of equipment	(29)	(643)
Purchases of marketable securities	(15,699)	(21,509)
Maturities of marketable securities	23,993	27,844
Net cash provided by investing activities	8,265	5,692
Cash flows from financing activities:
Proceeds from issuance of common stock	22,122	0
Proceeds from exercise of options	1,222	3,031
Proceeds from issuance of common stocks under employee purchase plan	161	216
Proceeds from debt	0	4,791
Net cash provided by financing activities	23,505	8,038
Effect of exchange rate on cash	(43)	19
Increase (decrease) in cash and cash equivalents	8,799	(13,646)
Cash and cash equivalents, beginning of period	35,781	61,014
Cash and cash equivalents, end of period	44,580	47,368
Non-cash investing activities:
Net transfer of instruments from inventory to property and equipment	500	1,288
Supplemental cash flow information:
Interest paid	2,144	2,144
Income taxes paid, net of refunds	$ 0	$ 26