Earnings per Share (Computation of Basic and Diluted Earnings Per Share) (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]                      
Net Income $ 6,088 $ 6,451 $ 6,316 $ 5,715 $ 4,424 $ 6,366 $ 6,331 $ 5,662 $ 24,570 $ 22,783 $ 23,428
Dividends and undistributed earnings allocated to participating securities                 (75) [1] (64) [1] (60) [1]
Net income available to common shareholders                 $ 24,495 $ 22,719 $ 23,368
Weighted-average common shares outstanding for basic EPS                 7,450,980 7,634,455 7,646,861
Dilutive effect of stock-based awards                 19,613 [2] 18,815 [2] 14,412 [2]
Weighted-average common and potential common shares for diluted EPS                 7,470,593 7,653,270 7,661,273
Basic EPS $ 0.82 $ 0.87 $ 0.85 $ 0.76 $ 0.58 $ 0.83 $ 0.83 $ 0.74 $ 3.29 $ 2.98 $ 3.06
Diluted EPS $ 0.82 $ 0.86 $ 0.85 $ 0.75 $ 0.58 $ 0.83 $ 0.82 $ 0.74 $ 3.28 $ 2.97 $ 3.05
Shares that were not considered in computation of potential common shares for purposes of diluted EPS                 36,250 [3] 15,250 [3] 49,500 [3]
[1] Represents dividends paid and undistributed earnings allocated to nonvested stock-based awards that contain non-forfeitable rights to dividends.
[2] Represents the effect of the assumed exercise of stock options, vesting of restricted shares, vesting of restricted stock units, and vesting of LTIP awards that have met the performance criteria, utilizing the treasury stock method.
[3] Represents stock-based awards not included in the computation of potential common shares for purposes of calculating diluted EPS, as the exercise prices were greater than the average market price of the Company's common stock.