Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended		106 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (9,961)	$ (33,048)	$ (91,870)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	568	545	1,913
Non-cash derivatives (gain) loss	(4,132)	18,871	27,278
Non-cash interest expense			985
Non-cash loss from modification of warrants		765	765
Common stock issued to 401(k) plan	118	124	443
Common stock issued for services	282		516
Share-based compensation expense	2,278	2,201	8,447
Changes in operating assets and liabilities:
Restricted cash	230		(372)
Prepaid expenses	(322)	26	(353)
Other assets	3	3	(192)
Accounts payable	(188)	(445)	711
Accrued interest payable	21		6
Accrued expenses	38	242	1,330
Net cash used in operating activities	(11,065)	(10,716)	(50,393)
Cash flows from investing activities:
Purchases of property and equipment	(14)	(651)	(3,534)
Net cash used in investing activities	(14)	(651)	(3,534)
Cash flows from financing activities:
Proceeds from issuance of note payable		150	150
Repayment of note payable	(55)		(112)
Proceeds from issuance of convertible notes payable			4,181
Proceeds from convertible bridge notes			500
Principal payments on capital lease obligation	(3)	(25)	(94)
Proceeds from loan payable		342	2,241
Repayment of loan payable, net			(321)
Proceeds from issuance of common stock and warrants	14,791	16,408	65,016
Net cash provided by financing activities	14,733	16,875	71,561
Increase in cash and cash equivalents	3,654	5,508	17,634
Cash and cash equivalents at beginning of period	13,980	12,825
Cash and cash equivalents at end of period	17,634	18,333	17,634
Supplemental disclosure of cash flow information and non-cash transactions:
Cash paid for interest	77	91	359
Conversion of convertible notes payable and accrued interest into common stock			4,672
Conversion of convertible bridge note payable and accrued interest into common stock			505
Asset acquired through capital lease obligation			94
Beneficial conversion feature on convertible and bridge notes payable			134
Fair value of warrants issued with bridge notes payable			179
Fair value of warrants issued in connection with loan agreement			42
Fair value of warrants issued in connection with underwriting agreement	6,848		6,848
Reclassification of derivative warrant liability to additional paid-in capital		$ 33,456	$ 38,104