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Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified | 9 Months Ended | 12 Months Ended
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Sep. 30, 2012 | Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Gross unrealized losses related to available for sale securities | Less than $1 thousand | Less than $1 thousand
Gross unrealized losses | $ (29,645) |
Maximum [Member] | Mortgage Backed Securities - Residential [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Gross unrealized losses | $ 1 | 1

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- Definition Gross unrealized losses related to available for sale securities. + References No definition available. + Details
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- Definition The net amount of gross unrealized gains (losses) for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563 + Details
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