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Stock-Based Compensation Plans - Summary of Nonvested Stock Option Activity (Details) - Nonvested Stock Option [Member] - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]    
Beginning Balance [1] 432,035  
Vested (344,535)  
Forfeited (5,250)  
Ending Balance [1] 82,250.00000  
Nonvested, Weighted Average Exercise Price (in usd per share) [1] $ 39.81 $ 39.91
Vested, Weighted Average Exercise Price (in usd per share) 39.93  
Forfeited, Weighted Average Exercise Price (in usd per share) $ 39.81  
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees 279,000 746,140
[1] Excludes 279,000 and 746,140 of stock options issued to retirement-eligible employees as of December 31, 2015 and 2014, respectively, as they are fully vested.