Reinsurance (Detail) (Property Casualty, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property Casualty
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount	$ 929,778	$ 916,817	$ 966,251
Ceded to other companies	354,418	333,263	343,663
Assumed from other companies	178,438	70,384	78,667
Net amount	$ 753,798	$ 653,938	$ 701,255
Percentage of amount assumed to net	24.00%	11.00%	11.00%

Amount of premiums assumed from other companies.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 2

-Subparagraph (SX 210.12-17)

-URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574992-122915

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAmountAssumedFromOtherCompanies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of premiums ceded to other companies.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAmountCededToOtherCompanies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Gross amount of premium revenue.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentGrossAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Net amount of gross premiums, less premiums ceded to other companies, plus premiums assumed from other companies; which represents the net amount of premium revenue on the income statement.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentNetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of amount of premiums assumed from other companies to net amount of premiums.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentPercentageOfAmountAssumedToNet
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SupplementaryInsuranceInformationBySegmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration