Condensed Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets
Equity securities	$ 870,950	$ 1,500,686
Debt securities	2,679,528	2,832,411
Short-term investments	1,096,517	264,811
Cash	84,749	76,741	32,526	18,125
Property and equipment - at cost, net of accumulated depreciation	17,906	19,504
Other assets	115,357	97,666
Net deferred tax receivable	80,975	77,147
Total assets	6,478,089	6,431,699	6,192,800
Liabilities and Stockholders' Equity
Senior Notes	299,035	298,923
Other liabilities	328,893	326,519
Current taxes payable	16,247	3,220
Total liabilities	3,552,412	3,522,831
Stockholders' equity	2,925,677	2,908,868	2,717,521	2,646,689
Liabilities and Equity	6,478,089	6,431,699
Parent Company
Assets
Equity securities	169,520	511,840
Debt securities		18,532
Short-term investments	361,273	103,086
Cash	3,826	889	1,831	77
Property and equipment - at cost, net of accumulated depreciation	670	847
Other assets	14,068	15,613
Current taxes receivable
Net deferred tax receivable	16,763	9,655
Investment in subsidiaries	2,755,719	2,618,653
Total assets	3,321,839	3,279,115
Liabilities and Stockholders' Equity
Senior Notes	299,035	298,923
Other liabilities	65,944	58,128
Current taxes payable	31,183	13,196
Total liabilities	396,162	370,247
Stockholders' equity	2,925,677	2,908,868
Liabilities and Equity	$ 3,321,839	$ 3,279,115