Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (33,314)	$ (18,346)	$ (38,756)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	689	752	740
Non-cash derivatives loss	10,804	376	18,871
Non-cash loss from modification of warrants			765
Common stock issued to 401(k) plan	201	173	192
Common stock issued for services		477
Share-based compensation expense	4,666	2,730	3,136
Changes in operating assets and liabilities:
Restricted cash	61	180
Prepaid expenses	888	(363)	124
Insurance receivable		(689)
Other assets	3	4	5
Accounts payable	(48)	(330)	(254)
Accrued expenses	(279)	(248)	271
Net cash used in operating activities	(16,329)	(15,284)	(14,906)
Cash flows from investing activities:
Non-cash disposals of property and equipment		45
Purchases of property and equipment	(5)	(47)	(749)
Net cash used in investing activities	(5)	(2)	(749)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,068	212	456
Proceeds from exercise of warrants	7,789	12	15,952
Proceeds from issuance of note payable			150
Repayment of notes payable	(18)	(56)	(57)
Principal payments on capital lease obligation		(21)	(33)
Proceeds from loan payable			342
Repayment of loan payable	(250)
Proceeds from issuance of common stock and warrants	14,480	14,618
Net cash provided by financing activities	23,069	14,765	16,810
Increase (decrease) in cash and cash equivalents	6,735	(521)	1,155
Cash and cash equivalents at beginning of period	13,459	13,980	12,825
Cash and cash equivalents at end of period	20,194	13,459	13,980
Supplemental disclosure of cash flow information and non-cash investing and financing transactions:
Cash paid for interest	121	132	125
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	$ 16,121		$ 33,456