Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 52,962us-gaap_NetIncomeLoss	$ 48,215us-gaap_NetIncomeLoss	$ 38,945us-gaap_NetIncomeLoss
Unrealized (loss) gain on available-for-sale securities arising during period	6,388	(8,244)	5,370
Reclassification adjustment for net gains	(1,156)	(764)	(954)
Other comprehensive income (loss), available-for-sale securities	5,232	(9,008)	4,416
Amortization of actuarial net gains	669	895	696
Recognition of unrealized gains (losses)	(4,584)	2,457	(1,119)
Change in underfunded pension liability	(3,915)	3,352	(423)
Other comprehensive (loss) income before income taxes	1,317	(5,656)	3,993
Tax effect	(486)	2,088	(1,508)
Other comprehensive (loss) income, net of tax	831	(3,568)	2,485
Comprehensive income, net of tax	$ 53,793us-gaap_ComprehensiveIncomeNetOfTax	$ 44,647us-gaap_ComprehensiveIncomeNetOfTax	$ 41,430us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount before tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit).

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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