Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Investment Income [Line Items]
Investment Income	$ 16,401	$ 15,033	$ 33,805	$ 29,419
Investment expenses	(753)	(787)	(1,547)	(1,516)
Net investment income	15,648	14,246	32,258	27,903
Fixed maturities
Net Investment Income [Line Items]
Investment Income	14,188	13,578	28,142	26,743
Equity Securities
Net Investment Income [Line Items]
Investment Income	1,971	1,257	5,204	2,288
Short-term investments
Net Investment Income [Line Items]
Investment Income	$ 242	$ 198	$ 459	$ 388