Earnings Per Common Share (Calculation of Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 40,824us-gaap_NetIncomeLoss	$ 36,153us-gaap_NetIncomeLoss	$ 35,074us-gaap_NetIncomeLoss
Less dividends and undistributed earnings allocated to participating securities	(152)	(156)	(161)
Net income applicable to common shareholders	40,672	35,997	34,913
Weighted average common shares outstanding - basic (in shares)	16,689,000	16,506,000	16,358,000
Basic earnings per common share (in dollars per share)	$ 2.44us-gaap_EarningsPerShareBasic	$ 2.18us-gaap_EarningsPerShareBasic	$ 2.13us-gaap_EarningsPerShareBasic
Less dividends and undistributed earnings allocated to participating securities	(151)	(155)	(160)
Net income applicable to common shareholers	$ 40,673	$ 35,998	$ 34,914
Dilutive effect of common stock equivalents (in shares)	183,000	158,000	43,000
Weighted average common shares outstanding - diluted (in shares)	16,872,000	16,664,000	16,401,000
Diluted earnings per common share (in dollars per share)	$ 2.41us-gaap_EarningsPerShareDiluted	$ 2.16us-gaap_EarningsPerShareDiluted	$ 2.13us-gaap_EarningsPerShareDiluted
Antidilutive common stock equivalents	59,234	23,286	357,179

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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