Gross Realized Gains and Losses on Sales and Calls of AFS Securities (Detail) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	$ 5,351	$ 17,670	$ 12,665	$ 56,524
Gross realized losses	(165)	(1,859)	(3,523)	(3,335)
Total Realized Gains on Sales and Calls of AFS Securities, net	5,587	15,811	9,452	53,189
Call Option
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	401		533
Gross realized losses			$ (223)

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 16
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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