Investment Securities Held-to-Maturity - Unrealized Gain (Losses) on Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,406,792	$ 1,487,884
Gross Unrealized Gains	13,892	2,424
Gross Unrealized Losses	7,081	25,859
Estimated Fair Value	1,413,603	1,464,449
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	251,617	291,779
Gross Unrealized Gains	2,707	185
Gross Unrealized Losses	249	5,043
Estimated Fair Value	254,075	286,921
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,155,175	1,196,105
Gross Unrealized Gains	11,185	2,239
Gross Unrealized Losses	6,832	20,816
Estimated Fair Value	$ 1,159,528	$ 1,177,528

Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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- Definition

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

+ References

+ Details

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

No definition available.

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Fair value of investments in debt securities classified 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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 50

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-Publisher FASB

-Name Accounting Standards Codification

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