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Securities - Additional Information (Detail)		3 Months Ended
		Mar. 31, 2016 USD ($) Investment	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Investment
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost	[1]	$ 551,247,000		$ 663,971,000
Gross realized losses		0	$ 0
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses		$ 19,100,000		$ 24,900,000
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost		39.10%		2.00%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost		$ 48,800,000		$ 1,200,000,000
Agency Debt Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment				7
Capital trust notes
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment		5		5
Mortgage-Related Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment		3		2
[1] Carrying value and estimated fair value are at cost.

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Number of Securities, Continuous Unrealized Loss Position More Than Twelve Months

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Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses.

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- Definition

Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Amortized Cost.

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- Definition

This item represents the gross loss realized on the sale of debt or equity securities 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 (a)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809

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