Change in Net Unrealized Gains/(Losses) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Gross unrealized gains (losses)	$ 44,529		$ (4,808)		$ 75,622
Deferred income tax charge (credit)	15,143		(1,324)		25,602
Change in net unrealized gains (losses) on investments, net of tax	29,386	[1]	(3,484)	[1]	50,020	[1]
Fixed maturities
Gross unrealized gains (losses)	44,712		(12,039)		59,667
Equity Securities
Gross unrealized gains (losses)	$ (183)		$ 7,231		$ 15,955

[1] Disclosure of reclassification amount, net of tax: Unrealized gains (losses) on investments arising during period $ 34,348 $ 12,339 $ 33,910 Reclassification adjustment for net realized gains (losses) included in net income (4,807 ) (16,797 ) 1,624 Reclassification adjustment for other-than-temporary impairment losses recognized in net income (155 ) 974 14,486 Change in net unrealized gains (losses) on investments, net of tax $ 29,386 $ (3,484 ) $ 50,020