Equity Compensation (Details 3) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Stock options    
Total fair value for the awards vested during the period $ 2,900,000  
Stock options    
Intrinsic-value    
Options Exercised 782,000  
Options Exercisable 14,232,000  
Options Vested and Expected to Vest $ 15,915,000  
Assumptions used to estimate fair value of stock options    
Expected dividends (as a percent) 0.00% 0.00%
Stock options | Minimum    
Assumptions used to estimate fair value of stock options    
Expected volatility (as a percent) 54.00% 56.00%
Expected term   3 years 9 months 18 days
Risk-free rate (as a percent) 1.30% 1.10%
Stock options | Maximum    
Assumptions used to estimate fair value of stock options    
Expected volatility (as a percent) 55.00% 60.00%
Expected term 6 years 1 month 6 days 6 years 1 month 6 days
Risk-free rate (as a percent) 1.60% 2.00%