CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (14,065)	$ (13,430)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	93	192
Non-cash interest expense	26	26
Stock-based compensation expense	1,207	1,266
Change in fair value of warrant liability	(102)	(3,123)
Loss on extinguishment of debt	221	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(126)	(596)
Restricted cash	(25)	0
Accounts payable	609	(578)
Accrued expenses and other liabilities	(991)	(1,209)
Deferred revenue	(406)	(55)
Net cash used in operating activities	(13,559)	(17,507)
Investing activities
Purchases of property and equipment	0	(286)
Net cash used in investing activities	0	(286)
Financing activities
Proceeds from issuance of common stock and common stock warrants, net of offering costs	0	12,172
Payments on notes payable	(14,124)	0
Proceeds from notes payable	0	5,000
Proceeds from exercise of common stock options and warrants	88	56
Net cash (used in) provided by financing activities	(14,036)	17,228
Net decrease in cash and cash equivalents	(27,595)	(565)
Cash and cash equivalents at beginning of period	36,079	54,059
Cash and cash equivalents at end of period	8,484	53,494
Supplemental non-cash financing activities
Issuance of warrants for common stock	0	328
Supplemental cash flow information
Cash paid for interest	$ 663	$ 374