Reinsurance (Detail) (Property Casualty, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property Casualty
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount	$ 1,034,658	$ 929,778	$ 916,817
Ceded to other companies	452,810	354,418	333,263
Assumed from other companies	251,807	178,438	70,384
Net amount	$ 833,655	$ 753,798	$ 653,938
Percentage of amount assumed to net	30.00%	24.00%	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

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Amount of premiums ceded to other companies.

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Gross amount of premium revenue.

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