Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 141,814	$ 140,434
Other comprehensive income (loss) before reclassifications	18,453	8,388
Amounts reclassified from accumulated other comprehensive income (loss)	(148)	(6,074)
Other comprehensive income (loss), net of tax	18,305	2,314
Ending Balance	160,119	142,748
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	190,589	146,672
Other comprehensive income (loss) before reclassifications	17,316	7,951
Amounts reclassified from accumulated other comprehensive income (loss)	(148)	0
Other comprehensive income (loss), net of tax	17,168	7,951
Ending Balance	207,757	154,623
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(48,775)	(26,131)
Other comprehensive income (loss) before reclassifications	1,137	437
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive income (loss), net of tax	1,137	437
Ending Balance	(47,638)	(25,694)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	0	19,893
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	(6,074)
Other comprehensive income (loss), net of tax	0	(6,074)
Ending Balance	$ 0	$ 13,819

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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