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Stock-based Compensation - Summary of Restricted Stock and Performance Share Units Activity (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested shares subject to performance condition 95,730    
Total fair value of shares vesting $ 9,900,000 $ 3,800,000 $ 1,800,000
Restricted Stock      
Beginning Balance (In Shares) 953,000    
Granted (In Shares) 375,000 379,000 261,000
Vested (In Shares) (325,000)    
Forfeited (In Shares) (56,000)    
Ending Balance (In Shares) 947,000 953,000  
Weighted Average Fair Value      
Beginning Balance (in dollars per share) $ 27.45    
Granted (in dollars per share) 29.27 $ 22.81 $ 31.78
Vested (in dollars per share) 28.09    
Forfeited (in dollars per share) 27.27    
Ending Balance (in dollars per share) $ 27.96 $ 27.45  
Performance Share Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of shares vesting $ 7,900,000 $ 3,400,000 $ 0
Restricted Stock      
Beginning Balance (In Shares) 693,000    
Granted (In Shares) 479,000    
Vested (In Shares) (81,000)    
Forfeited (In Shares) (269,000)    
Ending Balance (In Shares) 822,000 693,000  
Weighted Average Fair Value      
Beginning Balance (in dollars per share) $ 25.67    
Granted (in dollars per share) 27.00    
Vested (in dollars per share) 26.51    
Forfeited (in dollars per share) 25.74    
Ending Balance (in dollars per share) $ 26.31 $ 25.67