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Securities - Additional Information (Detail) $ in Thousands		9 Months Ended
		Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost	[1]		$ 586,355	$ 663,971
Proceeds from sales of held to maturity securities		$ 19,730
Gross realized gains from sales of held to maturity securities		$ 543
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses			$ 16,500	$ 24,900
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost			37.80%	2.00%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost			$ 43,700	$ 1,200,000
Minimum
Schedule of Investments [Line Items]
Percentage of amount collected to recognize sale of securities		85.00%
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				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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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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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27405-111563

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The cash inflow associated with the sale of securities that had been designated as held-to-maturity. Excludes proceeds from maturities, prepayments and calls by the issuer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26853-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 12
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