Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (25,870)	$ (27,364)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	119	304
Stock-based compensation expense	1,771	2,007
Accretion of discount/premium on investment securities	(6)	26
Non-cash interest expense	37	155
Gain on sale of fixed assets	(297)	(30)
Services received in non-monetary exchange	19
Changes in assets and liabilities:
Prepaid expenses and other current assets	(177)	(93)
Other assets	(85)
Accounts payable	662	(632)
Accrued expenses	396	(1,215)
Deferred rent	(81)	6
Other liabilities	47
Net cash used in operating activities	(23,465)	(26,836)
Investing activities
Purchases of short-term investments	(70,364)
Sales and maturities of short-term investments	48,090	14,910
Purchases of property and equipment		(57)
Sale of property and equipment	369	30
Net cash (used in) provided by investing activities	(21,905)	14,883
Financing activities
Proceeds from public offerings, net of issuance costs	38,886
Proceeds from at-the-market offering, net of issuance costs	8,253	8,036
Proceeds from exercise of common stock options and warrants	4	23
Payments on borrowing	(2,848)	(3,333)
Net cash provided by financing activities	44,295	4,726
Net decrease in cash, cash equivalents and restricted cash	(1,075)	(7,227)
Cash, cash equivalents and restricted cash, beginning of period	16,482	23,709
Cash, cash equivalents and restricted cash, end of period	15,407	16,482
Supplemental disclosure of cash flow information
Cash paid for interest	79	$ 327
Non-cash investing activities:
Fixed asset purchases included in accounts payable	18
Non-cash financing activities
At-the-market issuance costs included in accounts payable and accrued expenses	$ 110