Realized Gains And Losses Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 30,254	$ 4,761	$ 4,217	$ 1,842	$ 7,141	$ 3,238	$ 3,006	$ (1,389)	$ 41,074	$ 11,996	$ 41,319
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains									28,789	11,678	42,932
Losses									(1,915)	(7,044)	(3,239)
Net realized gains (losses)									26,874	4,634	39,693
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains									14,673	9,319	1,867
Losses									(473)	(1,957)	(241)
Net realized gains (losses)									$ 14,200	$ 7,362	$ 1,626