Schedule of Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Investment income	$ 9,601	$ 7,585	$ 28,722	$ 25,833
Investment expense	(749)	(1,058)	(2,488)	(3,345)
Net investment income	8,852	6,527	26,234	22,488
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Investment income	8,673	6,791	24,709	20,843
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Investment income	703	780	2,419	4,861
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Investment income	32	$ 14	59	42
Other Invested Assets
Schedule of Available-for-sale Securities [Line Items]
Investment income	$ 193		$ 1,535	$ 87