Fair Value Measurements, Warrant Liabilities, Changes in Level 3, and Outstanding Debt (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Reclassification of contingent warrant liability to equity upon exercise of warrants	$ (3,088)	$ (2,526)
Warrant Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	31,828
Reclassification of contingent warrant liability to equity upon exercise of warrants	(3,088)
Net increase in estimated fair value of contingent warrant liabilities upon revaluation	216
Ending balance	$ 28,956		$ 31,828
Warrant Liabilities [Member] | Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected volatility (in hundredths)	69.80%		69.60%
Risk-free interest rate (in hundredths)	0.29%		0.03%
Expected term	1 year 5 months 8 days		1 month 2 days
Warrant Liabilities [Member] | Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected volatility (in hundredths)	70.90%		72.90%
Risk-free interest rate (in hundredths)	0.69%		0.67%
Expected term	1 year 8 months 8 days		2 years 2 months 8 days
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing obligations	$ 48,004		$ 35,308
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing obligations	$ 49,686		$ 36,461