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Equity Incentive Plans - Assumptions Used Emplyee Stock Option Grants and Stock-Based Compensation to be Recognized (Details 3) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Employee stock options      
Weighted average of the assumptions used to compute employee stock based compensation      
Risk-free interest rate (as a percent) 1.92% 1.84% 1.73%
Expected volatility (as a percent) 75.00% 104.80% 104.80%
Expected dividend yield (as a percent) 0.00% 0.00% 0.00%
Expected life (in years) 6 years 3 months 6 years 3 months 6 years 3 months
Stock options      
Unrecorded deferred stock-based compensation      
Unrecorded deferred stock-based compensation balance related to stock options $ 6.2    
Weighted-average amortization period over which cost is expected to be recognized 1 year 9 months 15 days    
Options granted      
Weighted average grant date fair value of options granted (in dollars per share) $ 6.31