Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Investment Income [Line Items]
Investment Income	$ 16,582	$ 14,901	$ 50,386	$ 44,320
Investment expenses	(743)	(807)	(2,289)	(2,323)
Net investment income	15,839	14,094	48,097	41,997
Fixed maturities
Net Investment Income [Line Items]
Investment Income	14,401	13,399	42,540	40,142
Equity Securities
Net Investment Income [Line Items]
Investment Income	1,956	1,315	7,160	3,603
Short-term investments
Net Investment Income [Line Items]
Investment Income	$ 225	$ 187	$ 686	$ 575