Deferred Tax (Liabilities) Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Allowance for loan losses	$ 53,953	$ 45,521
Share-based compensation expense	11,478	9,786
Loan fee income	10,356	8,969
State income taxes	7,042	6,576
Net operating loss	8,175	6,089
Other accruals not currently deductible	2,205	6,010
Research and development credit	364	364
Other	16	16
Deferred tax assets	93,589	83,331
Valuation allowance	(8,539)	(6,453)
Net deferred tax assets after valuation allowance	85,050	76,878
Deferred tax liabilities:
Net unrealized gains on available-for-sale securities	(74,983)	(59,180)
Nonmarketable securities	(23,363)	(14,478)
Derivative equity warrant assets	(5,566)	(5,428)
Premises and equipment and other intangibles	(5,466)	(4,515)
FHLB stock dividend	(1,252)	(1,252)
Deferred tax liabilities	(110,630)	(84,853)
Net deferred tax (liabilities) assets	$ (25,580)	$ (7,975)