Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Operating activities
Net loss	$ (40,696)	$ (77,400)	$ (43,562)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	4,919	4,070	3,354
Stock-based compensation expense	17,458	11,475	11,369
Non-cash operating lease cost	2,831	0	0
Repayment of accrued interest of long-term debt	0	(5,446)	0
Gain on sale of business	(49,922)	0	0
Gain on equity securities	(625)	0	0
Loss on extinguishment of long-term debt	0	842	0
Amortization (accretion) of discount or premium on short-term investments	(204)	278	198
Amortization of deferred financing costs	810	438	171
Conversion of accrued interest to long-term debt	2,193	1,530	1,472
Loss on disposal of property and equipment	1,152	97	15
Provision for bad debt	(62)	467	361
Provision for inventory obsolescence	931	691	866
Changes in operating assets and liabilities
Accounts receivable	(9,805)	1,807	2,277
Inventory	(8,475)	5,251	(8,742)
Prepaid expenses and other assets	(3,350)	(2,714)	(1,278)
Accounts payable	(599)	4,640	(110)
Accrued liabilities	1,276	(494)	1,312
Accrued compensation and other employee benefits	3,567	3,463	295
Customer deposits	(1,778)	(778)	8,335
Deferred revenue	(6,536)	(1,779)	(29,161)
Operating lease liabilities	(2,506)	0	0
Deferred rent and other liabilities	0	(503)	1,171
Net cash used in operating activities	(89,421)	(54,065)	(51,657)
Investing activities
Purchases of property and equipment	(7,885)	(4,485)	(4,284)
Proceeds from sale of business	40,000	0	0
Proceeds from sale of short-term investments	2,500	7,910	3,600
Proceeds from maturity of short-term investments	97,970	51,300	79,599
Purchases of short-term investments	(147,744)	(77,650)	(81,405)
Net cash used in investing activities	(15,159)	(22,925)	(2,490)
Financing activities
Proceeds from long-term debt	20,000	60,000	0
Deferred costs related to long-term debt	100	500	0
Repayment of long-term debt and lease financing obligations	0	(45,000)	(58)
Fees paid upon extinguishment of debt	0	(1,009)	0
Proceeds from sale of common stock, net	68,273	53,829	56,486
Proceeds from issuance of common stock warrants	2,228	3,010	674
Proceeds from issuance of common stock for employee stock purchase plan	1,952	1,451	1,793
Tax withholdings related to net share settlements of restricted stock units	(1,474)	(207)	(313)
Proceeds from exercise of stock options	18,387	3,507	1,086
Net cash provided by financing activities	109,266	75,081	59,668
Net increase (decrease) in cash and cash equivalents	4,686	(1,909)	5,521
Effect of exchange rate changes on cash and cash equivalents	(9)	(14)	32
Cash and cash equivalents and restricted cash
Beginning of year	24,356	26,279	20,726
End of year	29,033	24,356	26,279
Cash and cash equivalents	29,033	24,356	26,136
Restricted Cash	0	0	143
Supplemental disclosures
Cash paid for interest	5,683	6,213	4,416
Fair value of warrants issued with long-term debt	968	1,583	0
Cash paid for taxes	265	231	154
Rental instruments reclassified from inventory	605	585	1,023
Operating lease right-of-use assets obtained in exchange for lease obligations	28,060	0	0
Common stock received for sale of a business	9,893	0	0
Non-cash inventory exchanged for services	$ 0	$ 106	$ 0