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Stock-Based Compensation (Restricted Stock) (Details) - Restricted Stock [Member] - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period (in years) 4 years    
Total fair value of restricted stock awards vested $ 8.8 $ 8.1 $ 6.8
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Nonvested, shares, beginning balance 306,442    
Nonvested, weighted-average grant date fair value, beginning balance (in dollars per share) $ 42.52    
Granted, shares [1] 159,442    
Granted, weighted-average grant date fair value (in dollars per share) [1] $ 62.54 $ 52.87 $ 43.45
Vested, shares (140,019)    
Vested, weighted-average grant date fair value (in dollars per share) $ 41.44    
Forfeited, shares (41,581)    
Forfeited, weighted-average grant date fair value (in dollars per share) $ 48.02    
Nonvested, shares, ending balance 284,284 306,442  
Nonvested, weighted-average grant date fair value, ending balance (in dollars per share) $ 53.11 $ 42.52  
[1] The restricted stock awards granted during 2015 are primarily related to our employee annual restricted stock award grant in March 2015.