Comprehensive Income - Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net effect on accumulated other comprehensive income for the period	$ 4,793	$ 3,124
Defined benefit pension plan (2):
Total reclassifications for the period	(397)	(198)
Amounts Reclassified From Accumulated Other Comprehensive Income/(Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities (gains) losses reclassified into earnings	(18)	78
Related income tax expense (benefit)	7	(29)
Net effect on accumulated other comprehensive income for the period	(11)	49
Amortization of unrealized gain transferred from available-for-sale	(107)	(138)
Related income tax expense	40	51
Net effect on accumulated other comprehensive income for the period	(67)	(87)
Defined benefit pension plan (2):
Amortization of net loss and prior service costs	790	374
Related income tax benefit	(315)	(138)
Net effect on accumulated other comprehensive income for the period	475	236
Total reclassifications for the period	$ 397	$ 198

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- Definition

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 of tax (expense) benefit 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 and 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 after tax and 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) 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 after tax of reclassification adjustments of other comprehensive income (loss).

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Other comprehensive income amortization of unrealized holding gain loss previously recognized in other comprehensive income before tax.

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Other comprehensive income amortization of unrealized holding gain loss previously recognized in other comprehensive income tax.

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Other comprehensive income loss held to maturity securities adjustment net of tax.

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