Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (28,581)	$ (9,961)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	527	568
Non-cash derivatives (gain) loss	11,349	(4,132)
Common stock issued to 401(k) plan	157	118
Common stock issued for services		282
Share-based compensation expense	3,614	2,278
Changes in operating assets and liabilities:
Restricted cash	61	230
Prepaid expenses	804	(322)
Other assets	3	3
Accounts payable	228	(188)
Accrued expenses	865	59
Net cash used in operating activities	(10,973)	(11,065)
Cash flows from investing activities:
Purchases of property and equipment	(2)	(14)
Net cash used in investing activities	(2)	(14)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,009
Repayment of loan payable, net	(155)	(55)
Proceeds from exercise of warrants	7,788
Repayment of notes payable	(18)
Principal payments on capital lease obligation		(3)
Proceeds from issuance of common stock and warrants	11,038	14,791
Net cash provided by financing activities	19,662	14,733
Increase (decrease) in cash and cash equivalents	8,687	3,654
Cash and cash equivalents at beginning of period	13,459	13,980
Cash and cash equivalents at end of period	22,146
Supplemental disclosure of cash flow information and non-cash investing and financing transactions:
Cash paid for interest	97	77
Fair value of warrants issued in connection with underwriting agreement		$ 6,848
Reclassification of derivative warrant liability to additional paid-in capital in connection with exercises	$ 16,122