Consolidated Statements of Comprehensive Earnings (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
NET EARNINGS	$ 89,559us-gaap_NetIncomeLoss	$ 78,868us-gaap_NetIncomeLoss	$ 74,225us-gaap_NetIncomeLoss
OTHER ITEMS OF COMPREHENSIVE EARNINGS (LOSS):
Change in unrealized gain (loss) on investment securities available-for-sale, before income tax	54,571	(69,054)	10,619
Reclassification adjustment for realized losses (gains) on investment securities included in net earnings, before income tax	4	(147)	(2,772)
Minimum liability pension adjustment, before income tax	2,540	6,209	(1,564)
Total other items of comprehensive earnings (losses)	57,115	(62,992)	6,283
Income tax benefit (expense) related to:
Investment securities	(19,101)	24,220	(2,746)
Minimum liability pension adjustment	(889)	(2,173)	547
Total income tax benefit (expense)	(19,990)us-gaap_OtherComprehensiveIncomeLossTax	22,047us-gaap_OtherComprehensiveIncomeLossTax	(2,199)us-gaap_OtherComprehensiveIncomeLossTax
COMPREHENSIVE EARNINGS	$ 126,684us-gaap_ComprehensiveIncomeNetOfTax	$ 37,923us-gaap_ComprehensiveIncomeNetOfTax	$ 78,309us-gaap_ComprehensiveIncomeNetOfTax

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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 of tax expense (benefit), 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 other comprehensive income (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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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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