Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 4,339	$ 4,473	$ 9,935	$ 5,306
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	1,231	3,113	2,405	4,979
Losses	(1,518)	(56)	(2,090)	(2,106)
Net realized gains (losses)	(287)	3,057	315	2,873
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	112		26
Losses	(11)		(79)
Net realized gains (losses)	101		(53)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	4,753	1,416	11,078	3,336
Losses	(228)		(1,405)	(903)
Net realized gains (losses)	$ 4,525	$ 1,416	$ 9,673	$ 2,433