Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net Investment Income [Line Items]
Investment Income	$ 15,033	$ 16,701	$ 29,419	$ 33,371
Investment expenses	(787)	(924)	(1,516)	(6,336)
Net investment income	14,246	15,777	27,903	27,035
Fixed maturities
Net Investment Income [Line Items]
Investment Income	13,578	15,006	26,743	30,416
Equity Securities
Net Investment Income [Line Items]
Investment Income	1,257	994	2,288	1,941
Short-term investments
Net Investment Income [Line Items]
Investment Income	$ 198	$ 701	$ 388	$ 1,014