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Stock-Based Compensation Plans Options Activity (Details) - Stock Options - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock Options      
Outstanding as of December 31, 2016 1,330,183    
Exercised (411,292)    
Forfeited (14,574)    
Expired (26,115)    
Outstanding as of December 31, 2017 878,202 1,330,183  
Exercisable as of December 31, 2017 878,202    
Weighted Average Exercise Price      
Outstanding as of December 31, 2013 (usd per share) $ 10.98    
Exercised (usd per share) 11.45    
Forfeited (usd per share) 10.64    
Expired (usd per share) 13.97    
Outstanding as of December 31, 2014 (usd per share) 10.66 $ 10.98  
Exercisable as of December 31, 2016 (usd per share) $ 10.66    
Weighted Average Remaining Contractual Term, Outstanding 4 years 1 month 6 days    
Weighted Average Remaining Contractual Term, Exercisable 4 years 1 month 6 days    
Additional Disclosures [Abstract]      
Outstanding, Aggregate Intrinsic Value $ 6,400,000    
Exercisable, Aggregate Intrinsic Value 6,400,000    
Number of options exercised 411,292 $ 920,924 $ 490,151
Total intrinsic value of options exercised 2,955,000 4,619,000 1,442,000
Cash received from options exercised 4,644,000 10,240,000 4,936,000
Tax deduction realized from options exercised $ 2,825,000 $ 4,328,000 $ 1,389,000