Investments (Detail) - Analysis of net realized gains (losses) and the change in unrealized (losses) gains on investments (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net realized gains (losses) on investments	$ 20,803	$ (66,437)
Other Investments Securities [Member]
Gross realized gains	66,889	27,142
Gross realized losses on investments sold	(25,121)	(56,134)
Fixed Maturities And Short Term Investments And Cash And Cash Equivalents [Member]
OTTI on investments, net of amounts transferred to other comprehensive income	$ (20,965)	$ (37,445)