Reinsurance (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
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									$ 1,069,677	$ 972,844	$ 912,020
Ceded to other companies									455,985	396,639	346,172
Assumed from other companies									228,247	205,759	125,797
Net earned premiums	219,902	213,895	205,814	202,328	201,566	201,262	196,017	183,119	841,939	781,964	691,645
Property Casualty
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									1,127,331	1,034,658	929,778
Ceded to other companies									482,596	452,810	354,418
Assumed from other companies									243,187	251,807	178,438
Net earned premiums									$ 887,922	$ 833,655	$ 753,798
Percentage of amount assumed to net									27.00%	30.00%	24.00%