Tax Effects of Temporary Differences That Give Rise to Federal, Foreign, State and Local Deferred Tax Assets and Deferred Tax Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Loss reserve discount	$ 29,687	$ 31,687
Unearned premiums	22,860	19,253
Compensation related	5,285	2,695
State and local net deferred tax assets	499	242
Other	4,245	664
Total gross deferred tax assets	62,576	54,541
Less: Valuation allowance	(499)	(242)
Total deferred tax assets	62,077	54,299
Deferred tax liabilities:
Deferred acquisition costs	(16,903)	(16,939)
Net unrealized gains on securities	(36,200)	(32,782)
Other	(5,758)	(10,869)
Total deferred tax liabilities	(58,861)	(60,590)
Net deferred income tax asset (liability)	$ 3,216	$ (6,291)