Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	$ 16,670	$ 18,242
Investment expenses	(5,412)	(858)
Net investment income	11,258	17,384
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	15,411	17,192
Equity Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	947	783
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment Income	$ 312	$ 267