Summary of Significant Accounting Policies (Details) - Reconciliation of the warrant liability measured at fair value using Level 3 inputs (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reconciliation of the warrant liability measured at fair value using Level 3 inputs [Abstract]
Balance at beginning of period	$ 1,474	$ 939
Exercise of common stock warrants		(2,505)
Remeasurementof common stock warrants	529	2,051
Balance at end of period	$ 2,003	$ 485