Organization and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Net loss	$ 11,314	$ 17,952
Cash used in operations	5,323	8,405
Accumulated deficit	183,940		$ 172,505
Cash balance (not less than $9.0 million)	12,394	$ 11,550	$ 18,247	$ 2,279
Hercules Term Loan, Liquidity Covenant
Debt Instrument [Line Items]
Cash balance (not less than $9.0 million)	$ 9,000