Reinsurance (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
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 1,069,188	$ 1,131,680	$ 1,278,910
Ceded to Other Companies	367,441	384,538	452,999
Assumed From Other Companies	45,892	20,992	19,104
Net Amount	$ 747,639	$ 768,134	$ 845,015
Percentage of Amount Assumed to Net	6.10%	2.70%	2.30%