Summary of Significant Accounting Policies (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income (loss) per share - Basic:
Net loss	$ (3,372)	$ (6,012)	$ (2,257)	$ (14,009)	$ (5,742)	$ (6,605)	$ (14,637)	$ (4,570)	$ (25,650)	$ (31,554)	$ (12,711)
Denominator for basic income (loss) per share (in shares)									40,789,445	29,830,207	8,965,098
Basic income (loss) per common share (in dollars per share)	$ (0.08)	$ (0.15)	$ (0.06)	$ (0.35)	$ (0.15)	$ (0.24)	$ (0.63)	$ (0.17)	$ (0.63)	$ (1.06)	$ (1.42)
Income (loss) per share - Diluted:
Net loss	(3,372)	(6,012)	(2,257)	(14,009)	(5,742)	(6,605)	(14,637)	(4,570)	(25,650)	(31,554)	(12,711)
Adjust: Fair value of dilutive warrants outstanding									2,840	2,270	11,091
Numerator for diluted income (loss) per share (in dollars)									$ (28,490)	$ (33,824)	$ (23,802)
Denominator for basic income (loss) per share (in shares)									40,789,445	29,830,207	8,965,098
Plus: Incremental shares underlying "in the money" warrants outstanding (in shares)									179,954	366,409	181,962
Denominator for diluted income (loss) per share (in shares)									40,969,399	30,196,616	9,147,060
Diluted income (loss) per common share (in dollars per share)	$ (0.09)	$ (0.17)	$ (0.09)	$ (0.35)	$ (0.15)	$ (0.31)	$ (0.63)	$ (0.18)	$ (0.70)	$ (1.12)	$ (2.60)