CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows From Operating Activities:
Net loss	$ (16,902)	$ (51,675)	$ (65,772)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	2,917	3,321	4,051
Depreciation and amortization of property and equipment	2,059	1,750	1,363
Amortization of patents and other intangiable assets	2,132	1,737	1,660
Changes in fair value of earnout, derivative and warrant liabilities	(958)	(387)	(509)
Amortization of senior debt issuance costs and discounts	1,469	961	1,316
Amortization of short-term investment purchase discounts	(90)	(131)	(126)
Deferred interest on debt			2,111
(Gain) loss on sale of equipment	(3)		(23)
Other adjustments	(12)	48	(91)
Changes in operating assets and liabilities:
Accounts receivable	1,238	(14,130)	(7,536)
Inventories	(643)	1,365	(6,190)
Deferred contract sales organization fees			720
Other assets	(63)	(444)	(414)
Accounts payable	(6,197)	1,270	3,008
Accrued expenses	4,368	14,874	13,171
Operating lease liabilities	(98)
Net cash used in operating activities	(10,783)	(41,441)	(53,261)
Cash Flows From Investing Activities:
Purchases of short-term investments	(17,231)	(17,906)	(48,015)
Sales and maturities of short-term investments	9,258	36,491	45,118
Proceeds from sale-leaseback of equipment			3,222
Proceeds from sale of equipment	2
Capital expenditures	(1,088)	(1,361)	(2,497)
Intangible asset expenditures	(59)	(5)	(361)
Net cash (used in) provided by investing activities	(9,118)	17,219	(2,533)
Cash Flows From Financing Activities:
Proceeds from the issuance of common stock, net of issuance costs	11	47,292	64,560
Payments made on borrowings	(8,598)	(8,425)	(989)
Proceeds from short-term line of credit	14,000
Payments made on short-term line of credit	(14,000)
Payment of debt financing costs	(1,158)	(90)	(40)
Payments made to purchase treasury stock			(120)
Payment of payroll taxes withheld for releases of restricted stock units	(2)	(46)
Net cash (used in) provided by financing activities	(9,747)	38,731	63,411
(Decrease) increase in cash and cash equivalents	(29,648)	14,509	7,617
Cash and Cash Equivalents:
Beginning	46,478	31,969	24,352
Ending	16,830	46,478	31,969
Supplemental Disclosure of Noncash Transactions:
Acquired equipment under finance lease	406
Finance lease liability from purchase of equipment	406	105
Derivative liability incurred in connection with Loan and Security Agreement	69
Deferred debt financing costs included in accounts payable and accrued expenses	119
Exit Fee liability incurred in connection with Second Amendment to Facility		750
Derivative Liability incurred in connection with Amendments to Facility		611	2,107
Prepaid assets included in accounts payable and accrued expenses			654
Issuance of senior secured convertible notes in lieu of interest payment			6,586
Issuance of common stock upon conversion of senior secured convertible notes			6,586
Capital lease liability from sale-leaseback transactions			3,222
Beneficial conversion feature incurred on convertible notes			613
Supplemental Cash Flow Information:
Interest paid	$ 6,565	$ 8,158	$ 6,769