Derivative Instruments (Detail) - Earnings relating to derivative instruments not formally designated as hedging instruments (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Total derivatives not designated as hedging instruments	$ 3,141	$ 2,346
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	(2,439)	1,221
Net realized and unrealized gains (losses) on derivative instruments	702	3,567
Investment Related Derivatives [Member]
Interest rate exposure	700	168
Foreign exchange exposure	(354)	6,437
Credit exposure	(3,699)	(1,253)
Financial market exposure	3,944	1,156
Financial Operations Derivatives [Member]
Credit exposure	143	182
Other Non-Investment Derivatives [Member]
Contingent credit facility	0	(2,030)
Guaranteed minimum income benefit contract	2,015	2,309
Modified coinsurance funds withheld contract	392	(4,623)
Derivatives Not Designated As Hedging Instruments [Member]
Net realized and unrealized gains (losses) on derivative instruments	$ 702	$ 3,567