Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (22,064)	$ (23,540)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	16	14
Noncash stock based compensation	2,727	2,607
Noncash interest	520	759
Change in fair value of warrants	(82)	(168)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	1,606	595
Accounts payable and accrued expenses	(1,473)	(648)
Net cash used in operating activities	(18,750)	(20,381)
Cash flows from investing activities
Acquisition of property and equipment	(771)	(25)
Net cash used in investing activities	(771)	(25)
Cash flows from financing activities
Cash paid for debt financing costs		(175)
Principal payments on long-term debt	(4,035)	(985)
Return of principal payments on long-term debt		985
Proceeds from the issuance of common stock, net	18,536	37,527
Proceeds from exercise of stock options	76	329
Net cash provided by financing activities	14,577	37,681
Net (decrease) increase in cash and cash equivalents	(4,944)	17,275
Cash and cash equivalents, beginning of period	48,750	34,395
Cash and cash equivalents, end of period	43,806	51,670
Supplemental cash flow information
Interest paid	$ 1,023	$ 1,125