Deferred Tax (Liabilities) Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets:
Allowance for loan losses	$ 45,521	$ 40,633
Share-based compensation expense	9,786	8,062
Loan fee income	8,969	7,533
State income taxes	6,576	3,636
Net operating loss	6,089	3,992
Other accruals not currently deductible	6,010	2,601
Research and development credit	364	237
Premises and equipment and other intangibles		2,096
Derivative equity warrant assets		1,270
Original issuance discount on 2008 convertible notes		1,212
Other	16	18
Deferred tax assets	83,331	71,290
Valuation allowance	(6,453)	(4,229)
Net deferred tax assets after valuation allowance	76,878	67,061
Deferred tax liabilities:
Net unrealized gains on available-for-sale securities	(59,180)	(16,696)
Nonmarketable securities	(14,478)	(6,965)
Derivative equity warrant assets	(5,428)
Premises and equipment and other intangibles	(4,515)
FHLB stock dividend	(1,252)	(1,251)
Other		(278)
Deferred tax liabilities	(84,853)	(25,190)
Net deferred tax (liabilities) assets	$ (7,975)	$ 41,871