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Consolidated Statements of Changes in Stockholders' Equity Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Statement of Stockholders' Equity [Abstract]      
Dividends on perferred stock (in dollars per share) $ 850 $ 407 $ 455
Dividends on common stock (in dollars per share) $ 0.42 $ 0.40 $ 0.38
Issuance of preferred stock (in shares) 1,650 3,850 0
Issuance of common shares pursuant to the Dividend Reinvestment Plan (in shares) 53,944 44,521 38,494
Issuance of common shares pursuant to the Deferred Compensation Plan (in shares) 6,048 5,920 4,766
Issuance of common shares pursuant to the First Retirement & Savings Plan (in shares) 19,366 9,693 19,414
Issuance of restricted common shares pursuant to the 2007 Stock Incentive Plan (in shares) 5,320 4,436 0
Purchase of treasury shares (in shares) 165,117 128,073 136,380
Issuance of common shares pursuant to the exercise of stock options (in shares) 44,763 11,392 49,500