Investments (Detail) - Fair values and amortized cost of held to maturity fixed maturities (USD $) In Thousands	Jun. 30, 2011	Dec. 30, 2010
Fixed maturities
Cost or Amortized Cost	$ 2,843,371	$ 2,728,335
Gross Unrealized Gains	24,394	38,982
Gross Unrealized Losses	(48,260)	(24,691)
Fair Value	2,819,505	2,742,626
US Government And Government Related [Member]
Fixed maturities
Cost or Amortized Cost	10,832	10,541
Gross Unrealized Gains	61	164
Gross Unrealized Losses	(2)	(9)
Fair Value	10,891	10,696
Corporate Debt Securities [Member]
Fixed maturities
Cost or Amortized Cost	1,369,317	1,337,797
Gross Unrealized Gains	6,349	6,370
Gross Unrealized Losses	(25,531)	(16,325)
Fair Value	1,350,135	1,327,842
Residential Mortgage Backed Securities Non Agency [Member]
Fixed maturities
Cost or Amortized Cost	84,730	82,763
Gross Unrealized Gains	321	634
Gross Unrealized Losses	(257)	(546)
Fair Value	84,794	82,851
Other Asset Backed Securities [Member]
Fixed maturities
Cost or Amortized Cost	293,700	287,109
Gross Unrealized Gains	3,345	1,134
Gross Unrealized Losses	(1,266)	(1,410)
Fair Value	295,779	286,833
NonUS Sovereign Government Supranational And Government Related [Member]
Fixed maturities
Cost or Amortized Cost	1,084,792	1,010,125
Gross Unrealized Gains	14,318	30,680
Gross Unrealized Losses	(21,204)	(6,401)
Fair Value	$ 1,077,906	$ 1,034,404