Summary of Activity in Reserve for Losses and Loss Adjustment Expenses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]
Net reserves for losses and LAE at beginning of year	$ 1,216,909	$ 1,237,234	$ 1,142,542
Provision for losses and LAE for claims occurring in the current year	520,227	542,724	474,852
Increase (decrease) in estimated losses and LAE for claims occurring in prior years	(1,266)	(45,291)	2,145
Incurred losses and LAE	518,961	497,433	476,997
Losses and LAE paid for claims occurring during:
Current year	(147,758)	(110,373)	(73,242)
Prior years	(365,479)	(407,385)	(309,063)
Losses and LAE payments	(513,237)	(517,758)	(382,305)
Net reserves for losses and LAE at end of year	1,222,633	1,216,909	1,237,234
Reinsurance recoverables on unpaid losses and LAE	822,438	880,139	845,445
Gross reserves for losses and LAE at end of year	$ 2,045,071	$ 2,097,048	$ 2,082,679