Significant Accounting Policies - Net Loss per Share and Fair Value Measurements (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Liability measured at fair value on a recurring basis
Warrant liability	$ 1,537		$ 3,072
Potentially dilutive common stock equivalents excluded from computation (in shares)	5.8	2.5
Fair Value, Inputs, Level 3
Liability measured at fair value on a recurring basis
Warrant liability	$ 1,537		$ 3,072