Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net loss	$ (14,961)	$ (15,736)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	11	9
Noncash stock based compensation	1,760	1,666
Noncash interest	360	344
Change in fair value of warrants	(102)	(130)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	2,243	1,617
Accounts payable and accrued expenses	(1,230)	(768)
Net cash used in operating activities	(11,919)	(12,998)
Cash flows from investing activities
Acquisition of property and equipment	(450)	(20)
Net cash used in investing activities	(450)	(20)
Cash flows from financing activities
Principal payments on long-term debt	(2,496)
Proceeds from the issuance of common stock, net		37,527
Proceeds from exercise of stock options	53	320
Net cash provided by (used in ) financing activities	(2,443)	37,847
Net increase (decrease) in cash and cash equivalents	(14,812)	24,829
Cash and cash equivalents, beginning of period	48,750	34,395
Cash and cash equivalents, end of period	33,938	59,224
Supplemental cash flow information
Interest paid	$ 713	$ 755