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Share-Based Payments - Summary of Restricted Stock Awards (Details) - Restricted Stock [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]      
Nonvested shares, Beginning Balance, Shares 618    
Nonvested shares, Beginning Balance, Weighted-Average Grant Date Fair Value $ 35.06    
Granted, Shares 504    
Granted, Weighted-Average Grant Date Fair Value $ 42.85 $ 33.56 $ 27.86
Vested, Shares (427)    
Vested, Weighted-Average Grant Date Fair Value $ 34.83    
Forfeited, Shares (22)    
Forfeited, Weighted-Average Grant Date Fair Value $ 39.22    
Nonvested shares, Ending Balance, Shares 673 618  
Nonvested shares, Ending Balance, Weighted-Average Grant Date Fair Value $ 40.90 $ 35.06