Schedule Of Changes In Assets Measured At Fair Value On Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Investment [Line Items]
Beginning Balance	$ 49,402		$ 104,841		$ 103,618
Included in realized gains/losses	1,482		(12,542)		500
Included in other comprehensive income	16,774		17,856		16,877
Acquisitions	183,676
Sales	(13,429)		(13,875)		(8,193)
Amortization	3,128		3,566		4,674
Other	1,536	[1]	1,442	[1]	1,353	[1]
Transfers out of Level 3	43,794		(51,886)		(13,988)
Ending Balance	286,363		49,402		104,841
Asset-backed Securities
Investment [Line Items]
Beginning Balance	7,122		8,042		7,981
Included in realized gains/losses	0		0		0
Included in other comprehensive income	1,078		(714)		255
Acquisitions	0
Sales	0		0		0
Amortization	(219)		(206)		(194)
Other	0	[1]	0	[1]	0	[1]
Transfers out of Level 3	0		0		0
Ending Balance	7,981		7,122		8,042
Collateralized Debt Obligations
Investment [Line Items]
Beginning Balance	30,320		22,456		18,037
Included in realized gains/losses	0		0		(1,712)
Included in other comprehensive income	12,067		3,952		2,445
Acquisitions	0
Sales	0		0		0
Amortization	2,648		2,470		2,333
Other	1,536	[1]	1,442	[1]	1,353	[1]
Transfers out of Level 3	0		0		0
Ending Balance	46,571		30,320		22,456
Corporates
Investment [Line Items]
Beginning Balance	11,250	[2]	73,673	[2]	71,764	[2]
Included in realized gains/losses	1,482	[2]	(12,542)	[2]	1,504	[2]
Included in other comprehensive income	3,600	[2]	14,578	[2]	14,711	[2]
Acquisitions	183,676	[2]
Sales	(13,429)	[2]	(13,875)	[2]	(5,862)	[2]
Amortization	699	[2]	1,302	[2]	2,536	[2]
Other	0	[1],[2]	0	[1],[2]	0	[1],[2]
Transfers out of Level 3	43,794	[2]	(51,886)	[2]	(10,980)	[2]
Ending Balance	231,072	[2]	11,250	[2]	73,673	[2]
Other Investments
Investment [Line Items]
Beginning Balance	710		670		5,836
Included in realized gains/losses	0		0		708
Included in other comprehensive income	29		40		(534)
Acquisitions	0
Sales	0		0		(2,331)
Amortization	0		0		(1)
Other	0	[1]	0	[1]	0	[1]
Transfers out of Level 3	0		0		(3,008)
Ending Balance	$ 739		$ 710		$ 670

[1] Includes capitalized interest and foreign exchange adjustments.

[2] Includes redeemable preferred stocks