Summary of Written Premium (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
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct									$ 1,127,331	$ 1,034,658	$ 929,778
Assumed									243,187	251,807	178,438
Ceded									(482,596)	(452,810)	(354,418)
Net	223,445	196,556	198,469	269,452	212,312	188,046	190,252	243,045	887,922	833,655	753,798
Direct									1,069,677	972,844	912,020
Assumed									228,247	205,759	125,797
Ceded									(455,985)	(396,639)	(346,172)
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
Direct									552,381	608,945	608,445
Assumed									155,313	151,137	81,945
Ceded									(188,733)	(262,649)	(213,393)
Net	$ 131,385	$ 125,086	$ 131,148	$ 131,342	$ 127,191	$ 128,850	$ 123,407	$ 117,985	$ 518,961	$ 497,433	$ 476,997