Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (12,853)	$ (15,567)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	276	272
Stock-based compensation	384	429
Change in fair value of warrant liability	(781)	5,787
Gain on sale of equipment	(13)	0
Non-cash interest expense	109	162
Asset impairment	97	0
Changes in operating assets and liabilities	(1,015)	(1,382)
Net cash used in operating activities	(13,796)	(10,299)
Investing activities
Purchases of property and equipment	(233)	(221)
Proceeds from sale of equipment	16	0
Net cash used in investing activities	(217)	(221)
Financing activities
Proceeds from issuance of common stock, net	440	0
Finance Lease, Principal Payments	(45)	0
Proceeds from equity offerings, net of issuance costs	0	14,026
Repayment of long-term debt	0	(841)
Proceeds from exercise of stock options	0	12
Net cash provided by financing activities	395	13,197
Net (decrease) increase in cash, cash equivalents and restricted cash	(13,618)	2,677
Cash, cash equivalents and restricted cash at beginning of period	40,758	26,677
Cash, cash equivalents and restricted cash at end of period	27,140	29,354
Non-cash financing activities and supplemental cash flow information
Right-of-use asset obtained in exchange for lease liabilities	5,931	1,686
Cash paid in connection with operating lease liabilities	394	406
Cash paid for interest	$ 261	$ 289