Loan and Lease Finance Receivables and Allowance for Loan Losses - Summary of Components of Loan and Lease Finance Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 549,776		$ 573,571
Commercial real estate	2,163,034		2,169,535
Construction	47,372		61,300
SFR mortgage	180,438		160,703
Dairy & livestock and agribusiness	264,663		342,311
Municipal lease finance receivables	105,246		105,767
Consumer and other loans	58,811		66,610
Gross loans	3,369,340		3,479,797
Purchase accounting discount	(17,526)		(25,344)
Deferred loan fees, net	(8,156)		(6,925)
Gross loans, net of deferred loan fees and discount	3,169,815		3,252,313
Less: Allowance for loan losses	(85,457)	(92,218)	(92,441)	(91,892)	(91,922)	(93,964)
Net loans	3,258,201		3,355,087
Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	525,144		547,422
Commercial real estate	2,008,746		1,990,107
Construction	46,365		59,721
SFR mortgage	180,123		159,288
Dairy & livestock and agribusiness	259,127		336,660
Municipal lease finance receivables	105,246		105,767
Consumer and other loans	53,220		60,273
Gross loans	3,177,971		3,259,238
Deferred loan fees, net	(8,156)		(6,925)
Gross loans, net of deferred loan fees and discount	3,169,815		3,252,313
Less: Allowance for loan losses	(85,457)		(92,441)
Net loans	3,084,358		3,159,872
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	24,632		26,149
Commercial real estate	154,288		179,428
Construction	1,007		1,579
SFR mortgage	315		1,415
Dairy & livestock and agribusiness	5,536		5,651
Consumer and other loans	5,591		6,337
Gross loans	191,369		220,559
Purchase accounting discount	(17,526)		(25,344)
Gross loans, net of deferred loan fees and discount	173,843		195,215
Net loans	$ 173,843		$ 195,215