Fair Value of Financial Assets and Liabilities - Derivative Instruments (Fair Value of Financial Liabilities Measured on Recurring Basis) (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	$ 10,032,000	$ 12,320,000
Fair value of warrant liability upon issuance	3,984,000	5,826,000
Total liabilities	$ 14,016,000	$ 18,146,000
Fair Value, Inputs, Level 1 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability
Fair value of warrant liability upon issuance
Total liabilities
Fair Value, Inputs, Level 2 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability
Fair value of warrant liability upon issuance
Total liabilities
Fair Value, Inputs, Level 3 [Member]
Schedule Of Derivative Liabilities At Fair Value [Line Items]
Preferred B stock conversion liability	$ 10,032,000	$ 12,320,000
Fair value of warrant liability upon issuance	3,984,000	5,826,000
Total liabilities	$ 14,016,000	$ 18,146,000