Amount And Percentage Of Fixed Maturities And Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011
Rating	AA
Fair Value	$ 1,943,563	$ 1,888,069
Percent of Total	100.00%
Extremely strong
Rating	AAA
Fair Value	316,690
Percent of Total	16.00%
Very strong
Rating	AA
Fair Value	1,076,193
Percent of Total	56.00%
Strong
Rating	A
Fair Value	411,864
Percent of Total	21.00%
Adequate
Rating	BBB
Fair Value	123,112
Percent of Total	6.00%
Speculative
Rating	BB & Below
Fair Value	11,833
Percent of Total	1.00%
Not rated
Rating	NR
Fair Value	$ 3,871
Percent of Total	0.00%

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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+ Details