Equity Compensation (Fair Value) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Stock options        
Total fair value for the awards vested during the period $ 1,400   $ 2,900  
Stock options        
Intrinsic-value        
Options Exercised     585 $ 1,039
Options Exercisable 4,553 $ 6,991 4,553 6,991
Options Vested and Expected to Vest $ 4,574 $ 7,266 $ 4,574 $ 7,266
Assumptions used to estimate fair value of stock options        
Expected volatility, minimum (as a percent)       53.00%
Expected volatility, maximum (as a percent)       55.00%
Expected volatility (as a percent) 62.00% 53.00% 62.00%  
Expected dividends (as a percent) 0.00% 0.00% 0.00% 0.00%
Expected term 6 years 1 month 6 days   6 years 1 month 6 days  
Risk-free rate (as a percent) 1.10%   1.10%  
Risk-free rate, minimum (as a percent)   1.50%   1.30%
Risk-free rate, maximum (as a percent)   1.80%   1.80%
Stock options | Minimum        
Assumptions used to estimate fair value of stock options        
Expected term   5 years 3 months 18 days   5 years 3 months 18 days
Stock options | Maximum        
Assumptions used to estimate fair value of stock options        
Expected term   6 years 1 month 6 days   6 years 1 month 6 days