Components of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Loans, principally due to allowance for loan losses	$ 27,148	$ 29,301
Stock-based compensation	5,486	4,637
Accrued expenses	12,813	8,968
Miscellaneous	5,369	4,257
Total deferred tax assets before valuation allowance	50,816	47,163
Valuation allowance	(2,775)	(2,605)
Total deferred tax assets	48,041	44,558
Deferred tax liabilities:
Net unrealized gain on securities available for sale	(49,319)	(46,877)
Land, buildings and equipment	(26,049)	(25,448)
Original issue discount	(4,505)
Intangibles	(3,430)	(2,771)
Miscellaneous	(4,802)	(3,409)
Total deferred tax liabilities	(88,105)	(78,505)
Net deferred tax liability	$ (40,064)	$ (33,947)