Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Jun. 30, 2017
Jun. 30, 2016
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 42,055       221,441   246,864 454,385  
Stock Repurchased and Retired During Period, In Total Dollars $ 1,999,000       $ 9,996,000   $ 11,995,000 $ 19,991,000  
Stock repurchased, common stock acquired, average cost per share $ 47.54       $ 45.14   $ 48.59 $ 44.00  
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased 2,519,620           2,519,620    
Common Stock [Member]                  
Shareholders' Equity [Line Items]                  
Dividends per share (in dollars per share) $ 0.15 $ 0.15 $ 0.15 $ 0.12 $ 0.12 $ 0.12 $ 0.30 $ 0.24