Related Party Transactions (Detail) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Premiums Written, Net	$ 1,398,253,000	$ 1,200,698,000	$ 3,202,207,000	$ 2,901,889,000
Reinsurance ContractsARX Holding Corporation [Member]
Premiums Written, Net	8,700,000	8,200,000
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	5,600,000	7,200,000
Related party reported acquisition costs	$ 5,200,000	$ 6,000,000

Premiums written for all insurance and reinsurance contracts, after adding premiums assumed from other insurers and subtracting any amounts ceded to another insurer.

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 Statement of Financial Accounting Standard (FAS)
-Number 113
-Paragraph 27
-Subparagraph a, b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (b),(c)
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration