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Share Repurchase Program Share Repurchse Program (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2018
Feb. 22, 2016
Equity [Abstract]    
Stock Repurchase Program, Authorized Amount $ 156,854  
Shares Paid for Tax Withholding for Share Based Compensation 36,736,000  
Accelerated Share Repurchases, Final Price Paid Per Share $ 45.42  
Stock Repurchased During Period, Shares 529,780  
Stock Repurchased During Period, Value $ 24,008  
Stock Repurchase Program, Remaining Authorized Repurchase Amount   $ 200,000
Treasury Stock Acquired, Average Cost Per Share $ 45.32  
Payments Related to Tax Withholding for Share-based Compensation $ 1,669