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Earnings Per Share (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jul. 27, 2017
Earnings Per Share [Line Items]          
Stock Repurchased During Period, Shares   92,987      
Treasury Stock Acquired, Average Cost Per Share   $ 32.90      
Stock Repurchase Program, Authorized Amount         $ 20,000
Stock Repurchase Program Expiration Date   Aug. 15, 2018      
Payments for Repurchase of Common Stock   $ 3,058 $ 101,483 $ 27,582  
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount $ 7,800 $ 7,800      
Increase In Basic Earnings Per Share From Change In Enacted Tax Rate $ 0.48 $ 0.48      
Increase In Diluted Earnings Per Share From Change In Enacted Tax Rate $ 0.47 $ 0.47      
Share Repurchase Program [Member]          
Earnings Per Share [Line Items]          
Stock Repurchased During Period, Shares   35,338      
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 19,300 $ 19,300      
Payments for Repurchase of Common Stock   $ 800      
Shares Repurchased Under Stock Compensation Program [Member]          
Earnings Per Share [Line Items]          
Stock Repurchased During Period, Shares   57,649      
Stock Repurchased During Period, Value   $ 2,200