Summary of Portfolio of Securities Available for Sale (Parenthetical) (Detail) (Available-for-sale capital securities and preferred stock, USD $)	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale capital securities and preferred stock
Schedule of Available-for-sale Securities [Line Items]
Non-credit portion of OTTI recorded in AOCL, before taxes	$ 570,000	$ 570,000

Accumulated Other Comprehensive Income Loss Noncredit Portion of Other Than Temporarily Impaired Securities Before Tax

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant