Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 518	$ 6,718	$ 10,453	$ 12,024
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	484	3,702	2,889	8,682
Losses	(667)	(1,645)	(2,757)	(3,752)
Net realized gains (losses)	(183)	2,057	132	4,930
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	9		109
Losses	(120)		(273)
Net realized gains (losses)	(111)		(164)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	1,107	6,109	12,185	9,445
Losses	(295)	(1,448)	(1,700)	(2,351)
Net realized gains (losses)	$ 812	$ 4,661	$ 10,485	$ 7,094