Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Investment Income [Line Items]
Investment Income	$ 14,901	$ 15,790	$ 44,320	$ 49,161
Investment expenses	(807)	(2,193)	(2,323)	(8,529)
Net investment income	14,094	13,597	41,997	40,632
Fixed maturities
Net Investment Income [Line Items]
Investment Income	13,399	14,364	40,142	44,779
Equity Securities
Net Investment Income [Line Items]
Investment Income	1,315	989	3,603	2,930
Short-term investments
Net Investment Income [Line Items]
Investment Income	$ 187	$ 437	$ 575	$ 1,452