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Stock-Based Compensation - Narrative - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares of common stock provided for awarding by the Plan (in shares) 20,150,000    
Number of shares available for issuance (in shares) 3,536,418    
Contractual term of award   10 years  
Award vesting period 5 years    
Stock-based compensation expense $ 33,600,000 $ 41,300,000 $ 61,100,000
Income tax benefit related to stock-based compensation expense 19,000,000 18,000,000 28,500,000
Unrecognized compensation expense 0    
Intrinsic value of options exercised $ 500,000 0 700,000
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Contractual term of award 10 years    
Award vesting period 5 years    
Restricted share awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation expense related to restricted share awards $ 70,200,000    
Weighted average recognition period 4 years 2 months    
Vesting-date fair value of shares vested and released $ 50,200,000 $ 47,000,000 $ 76,900,000
Weighted average grant-date fair value of restricted share awards granted (in dollars per share) $ 28.87 $ 19.06 $ 24.31
Restricted stock | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 1 year    
Restricted stock | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 15 years    
Performance units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Performance units | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of target grant potentially issuable depending on achievement of certain specified goals 0.00%    
Performance units | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of target grant potentially issuable depending on achievement of certain specified goals 200.00%