Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Sep. 30, 2015
Sep. 30, 2014
Feb. 07, 2014
Shareholders' Equity [Line Items]                    
Dividends per share (in dollars per share) $ 0.12       $ 0.12     $ 0.36 $ 0.36  
Stock Repurchase Program, Number of Shares Authorized to be Repurchased                   2,000,000
Stock Repurchase Program Number Of Shares Repurchased 204,590       434,993     204,590 881,979  
Stock Repurchased and Retired During Period, In Total Dollars $ 9,996,000       $ 19,987,000     $ 9,996,000 $ 39,972,000  
Stock repurchased, common stock acquired, average cost per share $ 48.86       $ 45.95     $ 48.86 $ 45.32  
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased 913,431             913,431    
Common Stock [Member]                    
Shareholders' Equity [Line Items]                    
Dividends per share (in dollars per share) $ 0.12 $ 0.12 $ 0.12 $ 0.12 $ 0.12 $ 0.12 $ 0.12