Investments (Additional Information) (Detail) - USD ($)	9 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Non Credit Portion Of Other Than Temporary Impairments Recognized In Other Comprehensive Income	$ 100,000
Investments available-for-sale book value	243,100,000	$ 212,900,000
Investments held-to-maturity book value	193,100,000	$ 202,400,000
Banks And Financial Institutions [Member]
Investment [Line Items]
Trust Preferred Securities Fair Value	1,000,000
Trust Preferred Securities	1,100,000
Government National Mortgage Association Certificates And Obligations Federal National Mortgage Association Certificates And Obligations And Federal Home Loan Mortgage Corporation Certificates And Obligations [Member] \| Collateralized Mortgage Obligations [Member]
Investment [Line Items]
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	142,000,000
Government National Mortgage Association Certificates And Obligations Federal National Mortgage Association Certificates And Obligations And Federal Home Loan Mortgage Corporation Certificates And Obligations [Member] \| Mortgage Backed Securities [Member]
Investment [Line Items]
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	$ 162,100,000

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 12

-Sentence Column A

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Non credit portion of other than temporary impairments recognized in other comprehensive income.

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- Definition

Trust Preferred Securities

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- Definition

Trust Preferred Securities Fair Value

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The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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The carrying amount as of the date of the latest financial statement presented of mortgage-related securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

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The carrying amount as of the date of the latest financial statement presented of mortgage-related securities classified as held to maturity which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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