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Compensation Plans - Schedule of Various Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 3,452 $ 3,427 $ 3,367
Weighted average fair value (usd per share) $ 50,190 $ 40,720  
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 174 $ 0 0
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense 1,211 898 850
Total fair value at vesting date 1,544 1,471 2,275
Total unrecognized compensation cost for nonvested stock units $ 2,175 $ 837 $ 1,084
Expected years to recognize unearned compensation 2 years 1 year 9 months 1 year 7 months
Stock Options and SSARs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Intrinsic value of option exercises on date of exercise $ 2,469 $ 3,156 $ 1,156
Cash received from the exercise of stock options $ 0 $ 91 $ 87
Stock Plan for Non-Management Directors      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares issued 11,750,000 10,531,000 12,528,000
Weighted average fair value (usd per share) $ 50.74 $ 42.46 $ 31.25