Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net loss	$ (18,004)	$ (28,581)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	417	527
Derivatives loss	788	11,349
Common stock issued to 401(k) plan	156	157
Share-based compensation expense	3,571	3,614
Changes in operating assets and liabilities:
Restricted cash		61
Prepaid expenses	(229)	804
Other assets	(308)	3
Accounts payable	35	228
Accrued expenses	1,248	865
Net cash used in operating activities	(12,326)	(10,973)
Cash flows from investing activities:
Purchases of property and equipment	(96)	(2)
Net cash used in investing activities	(96)	(2)
Cash flows from financing activities:
Proceeds from exercise of stock options	191	1,009
Proceeds from issuance of stock under ESPP	91
Repayment of loan payable	(294)	(155)
Repayment of note payable		(18)
Proceeds from exercise of warrants		7,788
Proceeds from issuance of common stock and warrants	29,905	11,038
Net cash provided by financing activities	29,893	19,662
Increase in cash and cash equivalents	17,471	8,687
Cash and cash equivalents at beginning of period	20,194	13,459
Cash and cash equivalents at end of period	37,665	22,146
Supplemental disclosure of cash flow information and non-cash transactions:
Cash paid for interest	76	97
Exercise of equity-classified warrants to common stock	$ 90	228
Reclassification of derivative warrant liability to additional paid-in capital		$ 16,122