Equity Compensation (Activity) (Details) - Stock options - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2016
Jun. 11, 2013
Shares Subject to Options Outstanding      
Balance at the beginning of the period (in shares)   4,572,672  
Granted (in shares) 0 50,000  
Exercised (in shares)   (619,757)  
Expired (in shares)   (69,832)  
Forfeited (in shares)   (51,588)  
Balance at the end of the period (in shares) 3,881,495 3,881,495  
Exercisable options (in shares) 2,990,429 2,990,429  
Vested and expected to vest at the end of the period (in shares) 3,822,911 3,822,911  
Weighted Average Grant Date Fair Value      
Granted (in dollars per share)   $ 4.63  
Weighted Average Exercise Price      
Balance at the beginning of the period (in dollars per share)   10.72  
Granted (in dollars per share)   8.16  
Exercised (in dollars per share)   4.87  
Expired (in dollars per share)   14.79  
Forfeited (in dollars per share)   15.68  
Balance at the end of the period (in dollars per share) $ 11.48 11.48  
Exercisable options at the end of the period (in dollars per share) 10.41 10.41  
Vested and expected to vest (in dollars per share) $ 11.44 $ 11.44  
Weighted-Average Remaining Contractual Life      
Exercisable options   5 years 7 months 6 days  
Vested and expected to vest   6 years 1 month 6 days  
2013 Plan      
Stock options      
Potential annual increase in shares authorized for issuance as a percentage of shares outstanding as of the preceding December 31     5.00%