Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (110,078)	$ (40,696)	$ (77,400)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	5,738	4,919	4,070
Stock-based compensation expense	19,374	17,458	11,475
Non-cash operating lease cost	3,238	2,831	0
Payment of accrued interest on long-term debt	(2,593)	0	(5,446)
Gain on sale of business	0	(49,922)	0
Loss (gain) on equity securities	300	(625)	0
Loss on extinguishment of long-term debt	7,143	0	842
Amortization (accretion) of discount or premium on short-term investments	(121)	(204)	278
Amortization of deferred financing costs	8,881	810	438
Conversion of accrued interest to long-term debt	0	2,193	1,530
Loss on disposal of property and equipment	119	1,152	97
Provision for inventory obsolescence and bad debt	886	869	1,158
Changes in operating assets and liabilities
Accounts receivable	(3,949)	(9,805)	1,807
Inventory	(4,909)	(8,475)	5,251
Prepaid expenses and other assets	4,321	(3,350)	(2,714)
Accounts payable	(3,170)	(599)	4,640
Accrued liabilities	(21)	1,276	(494)
Accrued compensation and other employee benefits	(936)	3,567	3,463
Cash payments received from customers	(4,758)	(1,778)	(778)
Deferred revenue and other liabilities	2,033	(6,536)	(2,282)
Operating lease liabilities	(3,160)	(2,506)	0
Net cash used in operating activities	(81,662)	(89,421)	(54,065)
Investing activities
Purchases of property and equipment	(7,457)	(7,885)	(4,485)
Proceeds from sale of business	0	40,000	0
Proceeds from sale of short-term investments	21,218	2,500	7,910
Proceeds from maturity of short-term investments	116,284	97,970	51,300
Purchases of short-term investments	(38,804)	(147,744)	(77,650)
Net cash provided by (used in) investing activities	91,241	(15,159)	(22,925)
Financing activities
Proceeds from long-term debt	230,000	20,000	60,000
Deferred costs related to long-term debt	7,403	100	500
Repayment of long-term debt and lease financing obligations	(80,000)	0	(45,000)
Fees paid upon extinguishment of debt	(4,845)	0	(1,009)
Proceeds from sale of common stock, net	215,765	68,273	53,829
Proceeds from issuance of common stock warrants	737	2,228	3,010
Proceeds from issuance of common stock for employee stock purchase plan	2,190	1,952	1,451
Tax withholdings related to net share settlements of restricted stock units	(2,012)	(1,474)	(207)
Proceeds from exercise of stock options	18,751	18,387	3,507
Repayment of finance lease obligations	(135)	0	0
Net cash provided by financing activities	373,048	109,266	75,081
Net increase (decrease) in cash and cash equivalents	382,627	4,686	(1,909)
Effect of exchange rate changes on cash and cash equivalents	188	(9)	(14)
Cash and cash equivalents
Beginning of year	29,033	24,356	26,279
End of year	411,848	29,033	24,356
Supplemental disclosures
Cash paid for interest	4,571	5,683	6,213
Fair value of warrants issued with long-term debt	0	968	1,583
Cash paid for taxes	357	265	231
Instruments reclassified from inventory to property and equipment	854	605	585
Finance lease right-of-use assets obtained in exchange for lease obligations	524	0	0
Operating lease right-of-use assets obtained in exchange for lease obligations	0	28,060	0
Common stock received for sale of a business	0	9,893	0
Non-cash inventory exchanged for services	$ 0	$ 0	$ 106