CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (25,406)	$ (17,278)	$ (28,569)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation	18	26	28
Amortization of warrant issuance costs	0	0	30
Stock-based compensation	4,055	3,986	5,398
Changes in assets and liabilities:
Prepaid expenses and other assets	258	382	451
Accounts payable	636	(1,392)	(477)
Other liabilities	0	140	0
Accrued payroll and related expenses	(1,856)	695	232
Accounts receivable	(6)	0	0
Related-party payable	0	0	(11)
Income tax liability	3	(3)	(4)
Deferred revenue	0	(1,500)	1,000
Net cash used in operating activities	(22,298)	(14,944)	(21,922)
Cash flows from investing activities:
Purchase of property and equipment	0	0	(13)
Purchase of investments	(3,090)	(946)	(10,527)
Proceeds from sale or maturity of investments	2,720	8,741	11,240
Net cash (used in) provided by investing activities	(370)	7,795	700
Cash flows from financing activities:
Proceeds from exercise of options	135	22	20
Proceeds from sale of common stock	27,051	3,677	19,196
Payments of taxes on cashless exercise of restricted stock units	(42)	(42)	(93)
Net cash provided by financing activities	27,144	3,657	19,123
Net increase (decrease) in cash and cash equivalents	4,476	(3,492)	(2,099)
Cash and cash equivalents, beginning of period	3,135	6,627	8,726
Cash and cash equivalents, end of period	7,611	3,135	6,627
Cash paid for income taxes	3	5	126
ASU Topic 606 [Member]
Cash flows from financing activities:
Deferred revenue reclassified to retained earnings - ASC 606 adoption	$ 2,500	$ 0	$ 0