Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Equity [Abstract]
Unrealized Gains on Securities Available for Sale, Balance at December 31, 2012	$ 16,961
Unrealized Gains on Securities Available for Sale, Current - period other comprehensive (loss) income	(1,922)
Unrealized Gains on Securities Available for Sale, Balance at March 31, 2013	15,039
Post Retirement Obligations, Balance at December 31, 2012	(9,245)
Post Retirement Obligations, Current - period other comprehensive (loss) income	259
Post Retirement Obligations, Balance at March 31, 2013	(8,986)
Accumulated Other Comprehensive Income, Balance at December 31, 2012	7,716
Accumulated Other Comprehensive Income, Current - period other comprehensive (loss) income	(1,663)
Accumulated Other Comprehensive Income, Balance at March 31, 2013	$ 6,053

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

+ References

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- Definition

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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- Definition

Net of tax amount of other comprehensive income (loss) attributable to the parent entity.

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