Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 9,186	$ 8,373	$ 12,812
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	5,681	4,756	8,326
Losses	(4,271)	(5,926)	(2,610)
Net realized gains (losses)	1,410	(1,170)	5,716
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	890	130
Losses	(1,552)	(383)
Net realized gains (losses)	(662)	(253)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	9,096	14,331	9,447
Losses	(658)	(4,535)	(2,351)
Net realized gains (losses)	$ 8,438	$ 9,796	$ 7,096