Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (8,153)	$ (12,177)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	10	12
Amortization	71
Noncash stock based compensation	969	2,106
Noncash interest		262
Change in fair value of warrants		(29)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	429	562
Accounts payable and accrued expenses	(590)	(644)
Lease liability	(75)
Net cash used in operating activities	(7,339)	(9,908)
Cash flows from investing activities:
Acquisition of property and equipment		(316)
Net cash used in investing activities		(316)
Cash flows from financing activities:
Proceeds from issuance of common stock in private placement, net of offering costs	7,810
Proceeds from At-the-Market sales of common stock, net of offering costs	2,249
Principal payments of loan payable		(3,263)
Proceeds from exercise of stock options	15
Net cash provided by (used in) financing activities	10,074	(3,263)
Net increase (decrease) in cash and cash equivalents	2,735	(13,487)
Cash and cash equivalents, beginning of period	7,851	35,952
Cash and cash equivalents, end of period	$ 10,586	22,465
Supplemental cash flow information
Interest paid		$ 449