Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Components of Loan and Lease Finance Receivables, Excluding PCI Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans, excluding PCI loans	$ 2,780,000
Gross loans, excluding PCI loans, net of deferred loan fees	3,817,067	3,546,231
Less: Allowance for loan losses	(59,825)	(75,235)
Total loans and lease finance receivables	3,757,242	3,470,996
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	390,011	376,800
SBA	134,265	135,992
Commercial real estate	2,487,803	2,207,515
Construction	55,173	47,109
SFR mortgage	205,124	189,233
Dairy & livestock and agribusiness	279,173	294,292
Municipal lease finance receivables	77,834	89,106
Consumer and other loans	69,884	55,103
Gross loans, excluding PCI loans	3,699,267	3,395,150
Less: Deferred loan fees, net	(8,567)	(9,234)
Gross loans, excluding PCI loans, net of deferred loan fees	3,690,700	3,385,916
Less: Allowance for loan losses	(59,825)	(75,235)	(92,441)	(93,964)
Net PCI loans	3,630,875	3,310,681
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	14,605	19,047
PCI Loans	133,496	173,104
SBA	1,110	1,414
Discount on PCI loans	(7,129)	(12,789)
Commercial real estate	109,350	141,141
Construction	0	644
SFR mortgage	205	313
Dairy & livestock and agribusiness	4,890	6,000
Municipal lease finance receivables	0	0
Consumer and other loans	3,336	4,545
Net PCI loans	$ 126,367	$ 160,315