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Employee Benefit Plans Employee Benefits Plan - Stock-Based Compensation - Valuation Assumptions (Details)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 4 years 7 months 25 days 4 years 8 months 12 days 4 years 8 months 12 days
Volatility 38.00% 40.00% 50.00%
Risk-free interest rate 1.50% 1.70% 0.90%
Dividend yield 0.00% 0.00% 0.00%
Employee Stock Purchase Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 6 months 6 months 6 months
Volatility 34.00% 32.00% 31.00%
Risk-free interest rate 0.30% 0.10% 0.20%
Dividend yield 0.00% 0.00% 0.00%