Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Overall default probabilities percentage		0.36%
Recovery and prepayment probabilities percentage		2.00%
Discount rate assumption	12.60%	12.60%
Pooled trust preferred security incurred credit-related other-than-temporary impairment ("OTTI")	$ 23	$ 95
Cumulative credit-related OTTI	517	517	422
Non-credit related OTTI recognized in other comprehensive income ("OCI")		300
Investments available-for-sale book value	202,800	202,800	255,400
Investments held-to-maturity book value	150,600	150,600	58,700
Banks and Financial Institutions
Investment [Line Items]
Trust preferred portfolio Fair Value	1,400	1,400
Trust preferred portfolio	1,700	1,700
Government National Mortgage Association Certificates and Obligations (GNMA)
Investment [Line Items]
Mortgage-backed portfolio	208,300	208,300
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	$ 312,500	$ 312,500

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Investments, Fair Value Assumptions, Discount Rate

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- Definition

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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- Definition

Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

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- Definition

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

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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=6475986&loc=d3e42546-110969

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- Definition

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

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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.

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

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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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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