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, 2011	Dec. 31, 2010
Deferred tax assets:
Loss reserve discount	$ 31,687	$ 30,190
Unearned premiums	19,253	14,358
Compensation related	2,695	5,149
State and local net deferred tax assets	242	2,185
Other	664	3,872
Total gross deferred tax assets	54,541	55,754
Less: Valuation allowance	(242)	(2,185)
Total deferred tax assets	54,299	53,569
Deferred tax liabilities:
Deferred acquisition costs	(16,939)	(11,645)
Net unrealized gains on securities	(32,782)	(17,638)
Other	(10,869)	(9,145)
Total deferred tax liabilities	(60,590)	(38,428)
Net deferred income tax asset (liability)	$ (6,291)	$ 15,141