CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net loss	$ (19,166)	$ (13,379)
Adjustments to reconcile net loss to net cash used for operating activities:
Depreciation and amortization expense	1,174	1,133
Stock compensation expense	10,095	5,739
Change in fair value of warrants	0	2,524
Loss on sale of fixed assets	0	23
Foreign currency translation loss	21	49
Amortization of premiums and discounts on marketable securities	(529)	0
Non-cash lease cost	2,011	0
Change in operating assets and liabilities:
Inventory	(3,265)	155
Accounts receivable	3,496	2,742
Prepaid and other current assets	(425)	(758)
Accounts payable	(1,895)	(1,212)
Accrued expenses	30	19
Operating lease liabilities	(1,804)	0
Other assets and liabilities, net	(76)	(58)
Net cash used in operating activities	(10,333)	(3,023)
Investing activities:
Purchases of short-term investments	(46,303)	(44,480)
Maturities of short-term investments	73,777	0
Expenditures for property, plant and equipment	(2,255)	(2,101)
Net cash provided by (used in) investing activities	25,219	(46,581)
Financing activities:
Net proceeds from equity offering	0	70,028
Net proceeds from common stock issuance due to stock option exercises	3,762	3,310
Proceeds from exercise of warrants	0	2,716
Other	(29)	(23)
Net cash provided by financing activities	3,733	76,031
Net increase in cash and cash equivalents	18,619	26,427
Cash and cash equivalents at beginning of period	18,286	26,862
Cash and cash equivalents at end of period	$ 36,905	$ 53,289