Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 1,049	$ 1,597
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	468	2,548
Losses	(1,256)	(1,127)
Net realized gains (losses)	(788)	1,421
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	112	268
Losses	(191)	(83)
Net realized gains (losses)	(79)	185
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	1,916	609
Losses	0	(618)
Net realized gains (losses)	$ 1,916	$ (9)