Investments (Detail) - Contractual maturities of held to maturity income securities (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Due less than 1 year	$ 5,071
Due less than 1 year	5,117
Due after 1 through 5 years	132,267	125,449
Due after 1 through 5 years	133,449	125,416
Due after 5 through 10 years	414,130	348,797
Due after 5 through 10 years	412,748	346,494
Due after 10 years	1,913,473	1,884,217
Due after 10 years	1,887,618	1,901,032
[HeldToMaturitySecuritiesDebtMaturitiesInFutureYearsAmortizedCost]	2,464,941	2,358,463
[HeldToMaturitySecuritiesDebtMaturitiesInFutureYearsFairValue]	2,438,932	2,372,942
Held to maturity income securities, Amortized Cost	2,843,371	2,728,335
Held to maturity income securities, Fair Value	2,819,505	2,742,626
Residential Mortgage Backed Securities Non Agency [Member]
Held to maturity income securities, Amortized Cost	84,730	82,763
Held to maturity income securities, Fair Value	84,794	82,851
Other Asset Backed Securities [Member]
Held to maturity income securities, Amortized Cost	293,700	287,109
Held to maturity income securities, Fair Value	295,779	286,833
Mortgage And Asset Backed Securities [Member]
Held to maturity income securities, Amortized Cost	378,430	369,872
Held to maturity income securities, Fair Value	$ 380,573	$ 369,684

This item represents the fair value of debt securities which are expected to mature after five years and through ten years from the balance sheet date and which are categorized as held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 20
-Subparagraph c
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 942
-SubTopic 320
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803

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This item represents the fair value of debt securities which are expected to mature after one year and through five years from the balance sheet date and which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 20
-Subparagraph b
-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 942
-SubTopic 320
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803

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This item represents the fair value of debt securities which are expected to mature after ten years from the balance sheet date which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 20
-Subparagraph d
-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 942
-SubTopic 320
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

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This item represents the fair value of debt securities which are expected to mature within one year of the balance sheet date and which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 20
-Subparagraph a
-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 942
-SubTopic 320
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803

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This item represents the amortized cost of investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity. The temporary impairments arise from the unrealized losses that are recognized in AOCI.

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This item represents the amortized cost of debt securities which are expected to mature after five years and through ten years from the balance sheet date and which are categorized as held-to-maturity.

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This item represents the amortized cost of debt securities which are expected to mature after ten years from the balance sheet date which are categorized as held-to-maturity.

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This item represents debt securities, at cost, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any, which are expected to mature in future years from the balance sheet date and which are categorized as held-to-maturity.

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