CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (77,702)	$ (78,208)	$ (84,305)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,518	2,997	2,602
Amortization of investment discount	226	99	(427)
Equity-based compensation expense	22,047	16,464	12,618
Amortization of debt discount and issuance costs	11,542	11,168	9,969
Realized loss on available-for-sale securities	0	3	0
(Gain) loss on disposal of property and equipment	(75)	785	837
Gain on extinguishment of debt	(9,793)	0	0
Inventory write-down	4,500	0	0
(Increase) decrease in assets:
Contributions to deferred compensation plan	(484)	(357)	0
Accounts receivable	(770)	1,592	(1,362)
Inventory	(415)	(1,356)	(3,655)
Prepaid expense and other assets	1,014	(2,087)	(752)
Increase (decrease) in liabilities:
Accounts payable	273	(1,006)	988
Accrued liabilities	(469)	(909)	(1,327)
Accrued interest	(283)	0	0
Deferred revenue and income	75	105	54
Deferred compensation	473	316	(34)
Net cash used in operating activities	(47,323)	(50,394)	(64,794)
Cash flows from investing activities:
Purchases of equipment	(603)	(1,362)	(330)
Purchase of marketable securities	(30,081)	(46,933)	(50,226)
Proceeds from sales of marketable securities	250	0	14,500
Maturities of marketable securities	38,738	61,901	88,867
Net cash provided by investing activities	8,304	13,606	52,811
Cash flows from financing activities:
Proceeds from issuance of common and preferred shares, net	42,880	359	1,458
Proceeds from exercise of options	1,620	5,703	4,907
Proceeds from issuance of common stocks under employee purchase plan	326	359	458
Proceeds from debt	0	5,578	0
Payment of debt	(360)	(366)	0
Payments of Stock Issuance Costs	(1,240)	0	0
Net cash provided by financing activities	43,226	11,633	6,823
Effect of exchange rate on cash	(90)	(78)	(86)
Increase (decrease) in cash and cash equivalents	4,117	(25,233)	(5,246)
Cash and cash equivalents, beginning of period	35,781	61,014	66,260
Cash and cash equivalents, end of period	39,898	35,781	61,014
Non-cash investing activities:
Net transfer of instruments from inventory to property and equipment	688	1,525	3,361
Supplemental cash flow information:
Interest paid	4,288	4,288	4,288
Income taxes paid, net of refunds	0	43	41
Extinguishment of Convertible Senior Notes through issuance of common stock	$ 38,902	$ 0	$ 0