Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Investment Income [Line Items]
Investment Income									$ 59,507	$ 64,634	$ 71,095
Investment expenses									(3,256)	(10,386)	(7,595)
Net investment income	14,254	14,094	14,246	13,657	13,616	13,597	15,777	11,258	56,251	54,248	63,500
Fixed maturities
Net Investment Income [Line Items]
Investment Income									53,898	58,995	65,060
Equity Securities
Net Investment Income [Line Items]
Investment Income									4,835	3,945	5,071
Short-term investments
Net Investment Income [Line Items]
Investment Income									$ 774	$ 1,694	$ 964