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Stock-Based Compensation Restricted Stock Units Summary (Details) - Restricted Stock Units (RSUs) [Member] - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
[Line Items]      
Outstanding, beginning balance, Number 556 701  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value $ 63.72   $ 47.68
Shares converted upon acquisition, number 579    
Shares converted upon acquisition, Weighted Average Grant Date Fair Value $ 69.40    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 136 131  
Weighted average fair value $ 69.30 $ 63.12  
Forfeited, Number (28) (3)  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value $ 68.44    
Outstanding, ending balance, Number 891 512  
Vested and Released [Member]      
[Line Items]      
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures 352 317  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value $ 47.18    
Released, Aggregate Intrinsic Value $ 17,231 $ 12,066  
Vested but Not Released [Member]      
[Line Items]      
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures 10    
Released, Aggregate Intrinsic Value $ 729    
Expected to Vest [Member]      
[Line Items]      
Outstanding, ending balance, Number 788    
Expected to vest, Aggregate Intrinsic Value $ 56,369    
Long Term Performance Restricted Stock Award [Member]      
[Line Items]      
Risk-free interest rate 2.20% 1.00%  
Expected term (years) 2 years 1 month 6 days 1 year 8 months 12 days  
Weighted average fair value $ 78.56 $ 77.78