Investments (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Investment [Line Items]
Overall default probabilities percentage	0.53%
Recovery and prepayment probabilities percentage	2.00%
Discount rate assumption	11.64%
Non-credit related OTTI recognized in other comprehensive income ("OCI")	$ 0.1
Investments available-for-sale book value	212.9	186.6
Investments held-to-maturity book value	202.4	165.8
Banks and Financial Institutions
Investment [Line Items]
Trust preferred portfolio Fair Value	1.2
Trust preferred portfolio	1.3
Government National Mortgage Association Certificates and Obligations (GNMA)
Investment [Line Items]
Mortgage-backed portfolio	167.7
Government National Mortgage Association Certificates and Obligations (GNMA) \| Federal Home Loan Mortgage and Federal National Mortgage Association \| Federal Home Loan Mortgage Corporation
Investment [Line Items]
Mortgage-backed portfolio	$ 193.9

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Rate at which investment are expected to prepay principal balances, used as an input to measure fair value.

+ References

No definition available.

+ Details

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- Definition

Percentage of investment will not be repaid and instead default, used as an input to measure fair value.

+ References

No definition available.

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- Definition

Investments, Fair Value Assumptions, Discount Rate

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No definition available.

+ Details

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- Definition

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

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No definition available.

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- Definition

Trust Preferred Securities

+ References

No definition available.

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- Definition

Trust Preferred Securities Fair Value

+ References

No definition available.

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- Definition

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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- Definition

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=34720971&loc=SL6224234-111729

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- Definition

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.

+ References

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