Fair Value of Financial Assets and Liabilities - Derivative Instruments (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	$ 19,425,000	$ 12,320,000
Warrant liability	14,727,000	5,826,000
Total liabilities	34,152,000	18,146,000
Fair Value, Inputs, Level 1 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	0	0
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	0	0
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 3 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	19,425,000	12,320,000
Warrant liability	14,727,000	5,826,000
Total liabilities	$ 34,152,000	$ 18,146,000