Supplementary Insurance Information (Detail) (Property and Casualty Insurance, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property and Casualty Insurance
Supplementary Insurance Information, by Segment [Line Items]
Deferred Policy Acquisition Costs	$ 70,537	$ 67,692	$ 71,098
Future Policy Benefits, Losses, Claims and Loss Expenses	2,313,035	2,328,742	2,520,979
Unearned Premiums	549,740	523,927	573,906
Other Policy Claims and Benefits Payable
Premium Revenue	747,639	768,134	845,015
Net Investment Income	117,424	128,878	116,719
Benefits, Claims, Losses and Settlement Expenses	429,986	377,937	442,104
Amortization of Deferred Policy Acquisition Costs	141,471	143,842	147,635
Other Operating Expenses	126,654	115,493	126,087
Premiums Written	$ 774,648	$ 736,154	$ 830,829