Debt - Outstanding Long-Term Debt (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Total debt, outstanding principal	$ 24,298,000	$ 24,500,000
Less: current portion, outstanding principal	(20,798,000)	(20,000,000)
Long-term debt, outstanding principal	3,500,000	4,500,000
Total debt, unamortized discount	(1,753,000)	(2,369,000)
Less: current portion, unamortized discount	1,032,000	930,000
Long-term debt, unamortized discount	(721,000)	(1,439,000)
Total debt, net carrying amount	22,545,000	22,131,000
Less: current portion, net carrying amount	(19,766,000)	(19,070,000)
Long-term debt	2,779,000	3,061,000
Hercules Term Loan
Debt Instrument [Line Items]
Total debt, outstanding principal	20,000,000	20,000,000	$ 20,000,000
Total debt, unamortized discount	(752,000)	(930,000)
Total debt, net carrying amount	19,248,000	19,070,000
Convertible Note
Debt Instrument [Line Items]
Total debt, outstanding principal	4,298,000	4,500,000
Total debt, unamortized discount	(1,001,000)	(1,439,000)
Total debt, net carrying amount	$ 3,297,000	$ 3,061,000