Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (78,208)	$ (84,305)	$ (88,326)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,997	2,602	2,561
Amortization of investment discount	99	(427)	(621)
Equity-based compensation expense	16,464	12,618	14,422
Amortization of debt discount and issuance costs	11,168	9,969	6,849
Realized loss on available-for-sale securities	3	0	0
Loss on disposal of property and equipment	785	837	678
(Increase) decrease in assets:
Contributions to deferred compensation plan	(357)	0	0
Accounts receivable	1,592	(1,362)	86
Inventory	(1,356)	(3,655)	(4,223)
Prepaid expense and other assets	(2,087)	(752)	(250)
Increase (decrease) in liabilities:
Accounts payable	(1,006)	988	(748)
Accrued liabilities	(909)	(1,327)	1,426
Accrued interest	0	0	1,262
Deferred revenue and income	105	54	(904)
Deferred compensation	316	(34)	32
Net cash used in operating activities	(50,394)	(64,794)	(67,756)
Cash flows from investing activities:
Purchases of equipment	(1,362)	(330)	(998)
Purchase of marketable securities	(46,933)	(50,226)	(120,556)
Proceeds from sales of marketable securities	0	14,500	3,000
Maturities of marketable securities	61,901	88,867	98,416
Net cash provided by (used in) investing activities	13,606	52,811	(20,138)
Cash flows from financing activities:
Proceeds from issuance of common stock	359	1,458	583
Proceeds from exercise of options and warrants	6,062	5,365	3,749
Proceeds from issuance of convertible note	0	0	171,500
Proceeds from debt	5,578	0	0
Payment of debt	(366)	0	0
Prepayment of forward stock repurchase transaction	0	0	(45,069)
Payment of debt issuance costs	0	0	(4,992)
Net cash provided by financing activities	11,633	6,823	125,771
Effect of exchange rate on cash	(78)	(86)	(130)
(Decrease) increase in cash and cash equivalents	(25,233)	(5,246)	37,747
Cash and cash equivalents, beginning of period	61,014	66,260	28,513
Cash and cash equivalents, end of period	35,781	61,014	66,260
Non-cash investing activities:
Net transfer of instruments from inventory to property and equipment	1,525	3,361	4,767
Supplemental cash flow information:
Interest paid	4,288	4,288	2,001
Income taxes paid, net of refunds	$ 43	$ 41	$ 651