Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Consolidated Statements of Comprehensive Income (Unaudited) [Abstract]
Net income	$ 10,715us-gaap_NetIncomeLoss	$ 11,011us-gaap_NetIncomeLoss
Net unrealized holding gain on securities available for sale	3,309	7,455
Reclassification adjustments for net gain recognized in income	(249)	(6)
Tax effect	(1,222)	(3,026)
Net unrealized gain on securities available for sale, net of tax	1,838	4,423
Amortization of net actuarial gain	(5)	(72)
Amortization of prior service credit	(22)	(45)
Tax effect	11	45
Amortization of net actuarial gain and prior service credit on pension and postretirement plans, net of tax	(16)	(72)
Other comprehensive income, net of tax	1,822	4,351
Comprehensive income	$ 12,537us-gaap_ComprehensiveIncomeNetOfTax	$ 15,362us-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 after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

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

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

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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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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