Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) - USD ($)
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Jul. 21, 2016
Shareholders' Equity [Line Items]            
Stock Repurchase Program, Number of Shares Authorized to be Repurchased           3,000,000
Stock Repurchased and Retired During Period, Shares 364,286       204,809  
Stock Repurchased and Retired During Period, In Total Dollars $ 19,993,000       $ 9,996,000  
Stock repurchased, common stock acquired, average cost per share $ 54.88       $ 48.81  
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased 1,454,379          
Common Stock [Member]            
Shareholders' Equity [Line Items]            
Dividends per share (in dollars per share) $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.15