Other Invested Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Other invested assets	$ 179,815		$ 207,294
Investment in Homesite
Condensed Financial Statements, Captions [Line Items]
Other invested assets	102,900		122,700
ORX Exploration, Inc.
Condensed Financial Statements, Captions [Line Items]
Other invested assets	26,900		27,600
Partnership Investment
Condensed Financial Statements, Captions [Line Items]
Other invested assets	23,600	[1]	24,800	[1]
Loans and other Investments
Condensed Financial Statements, Captions [Line Items]
Other invested assets	$ 26,400		$ 32,200

[1] Equity method partnership investments were dissolved during the third quarter of 2010, and thus were not outstanding as of December 31, 2010 and December 31, 2011.