Loss and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Reserve Balances, Net of Related Amounts Recoverable from Reinsurers (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract]
Reserves for loss and LAE at beginning of year	$ 570,450	$ 538,214	$ 532,204
Less amounts recoverable from reinsurers on unpaid loss and LAE	55,190	60,937	65,536
Reserves for loss and LAE, net of related amounts recoverable from reinsurers, at beginning of year	515,260	477,277	466,668
Add:
Provision for loss and LAE for claims occurring in the current year, net of reinsurance	241,584	222,393	196,269
Change in estimated loss and LAE for claims occurring in prior years, net of reinsurance	(12,611)	(2,490)	(6,563)	(3,100)	(3,900)	(2,300)
Incurred losses during the current year, net of reinsurance	228,973	219,903	189,706
Less loss and LAE payments for claims, net of reinsurance, occurring during:
Current year	44,474	50,423	53,213
Prior years	133,901	131,497	125,884
Claims Paid	178,375	181,920	179,097
Reserves for loss and LAE, net of related amounts recoverable from reinsurers, at end of year	565,858	515,260	477,277	466,668
Add amounts recoverable from reinsurers on unpaid loss and LAE	48,699	55,190	60,937	65,536
Reserves for loss and LAE	$ 614,557	$ 570,450	$ 538,214	$ 532,204