Realized Gains and Losses Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ (988)	$ 4,761	$ 7,171	$ 10,820
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	1,099	4,011	6,035	11,868
Losses	(2,087)	(216)	(2,470)	(1,746)
Net realized gains (losses)	(988)	3,795	3,565	10,122
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains		966	3,733	1,171
Losses			(127)	(473)
Net realized gains (losses)		$ 966	$ 3,606	$ 698