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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 1,586	$ 518	$ 5,143	$ 10,453
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	1,356	484	5,200	2,889
Losses	(1,221)	(667)	(3,086)	(2,757)
Net realized gains (losses)	135	(183)	2,114	132
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	128	9	803	109
Losses	(107)	(120)	(250)	(273)
Net realized gains (losses)	21	(111)	553	(164)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	1,443	1,107	3,123	12,185
Losses	(13)	(295)	(647)	(1,700)
Net realized gains (losses)	$ 1,430	$ 812	$ 2,476	$ 10,485