Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (19,810)	$ (21,867)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	111	237
Stock-based compensation expense	1,340	1,501
Accretion of discount/premium on investment securities	(4)	26
Non-cash interest expense	37	128
Gain on disposal of property and equipment	(297)	(30)
Services received in non-monetary exchange	8
Changes in assets and liabilities:
Prepaid expenses and other current assets	(120)	(98)
Accounts payable	274	(203)
Accrued expenses	267	(903)
Deferred rent	(3)	10
Net cash used in operating activities	(18,197)	(21,199)
Investing activities
Purchases of short-term investments	(39,364)
Sales and maturities of short-term investments	16,000	14,910
Purchases of property and equipment		(57)
Proceeds from sale of property and equipment	365	30
Net cash (used in) provided by investing activities	(22,999)	14,883
Financing activities
Proceeds from public offering, net of issuance costs	38,886
Proceeds from at-the-market offering, net of issuance costs	8,313	6,910
Proceeds from exercise of common stock options and warrants	4	23
Payments on borrowing	(2,500)	(2,500)
Net cash provided by financing activities	44,703	4,433
Net increase (decrease) in cash, cash equivalents and restricted cash	3,507	(1,883)
Cash, cash equivalents and restricted cash, beginning of period	16,482	23,709
Cash, cash equivalents and restricted cash, end of period	19,989	21,826
Supplemental disclosure of cash flow information
Cash paid for interest	$ 79	$ 269