Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net Investment Income [Line Items]
Investment Income	$ 17,404	$ 14,386
Investment expenses	(794)	(729)
Net investment income	16,610	13,657
Fixed maturities
Net Investment Income [Line Items]
Investment Income	13,953	13,167
Equity Securities
Net Investment Income [Line Items]
Investment Income	3,233	1,030
Short-term investments
Net Investment Income [Line Items]
Investment Income	$ 218	$ 189