Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	$ 14,386	$ 16,670
Investment expenses	(729)	(5,412)
Net investment income	13,657	11,258
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	13,167	15,411
Equity Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	1,030	947
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	$ 189	$ 312