CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Cash Flows From Operating Activities:
Net loss	$ (11,363)	$ (29,643)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	1,896	2,053
Depreciation and amortization of property and equipment	1,049	850
Amortization of patents and other intangible assets	1,052	869
Changes in fair value of earnout, derivative and warrant liabilities	(644)	(349)
Amortization of senior debt discounts	696	427
Amortization of short-term investment purchase discounts	(58)	(106)
Gain (loss) on sale of equipment	(2)	1
Other adjustments		(47)
Changes in operating assets and liabilities:
Accounts receivable	7,657	(4,306)
Inventories	(2,007)	(981)
Other assets	2,221	2,251
Accounts payable	(6,174)	(5,400)
Accrued expenses	(2,134)	13,184
Operating lease liabilities	(49)
Net cash used in operating activities	(7,860)	(21,197)
Cash Flows From Investing Activities:
Purchases of short-term investments	(7,193)	(17,904)
Sales and maturities of short-term investments	2,758	26,743
Capital expenditures	(365)	(814)
Intangible asset expenditures	(55)	(28)
Net cash (used in) provided by investing activities	(4,855)	7,997
Cash Flows From Financing Activities:
Proceeds from the issuance of common stock, net of issuance costs	11
Payments made on borrowings	(8,015)	(451)
Payment of payroll taxes withheld for releases of restricted stock units	(2)
Net cash used in financing activities	(8,006)	(451)
Decrease in cash and cash equivalents	(20,721)	(13,651)
Cash and Cash Equivalents:
Beginning	46,478	31,969	$ 31,969
Ending	25,757	18,318	$ 46,478
Supplemental Disclosure of Noncash Transactions:
Acquired equipment under finance lease	406	105
Finance lease liability from purchase of equipment	406	105
Supplemental Cash Flow Information:
Interest paid	$ 3,510	$ 4,116