Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Components of Loans and Lease Finance Receivables, Excluding PCI Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans, excluding PCI loans, net of deferred loan fees	$ 3,784,219		$ 3,817,067
Less: Allowance for loan losses	(59,554)	$ (60,709)	(59,825)	$ (60,974)	$ (68,725)	$ (75,235)
Total loans and lease finance receivables	3,724,665		3,757,242
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	406,423		390,011
SBA	120,566		134,265
Commercial real estate	2,569,411		2,487,803
Construction	46,927		55,173
SFR mortgage	214,503		205,124
Dairy & livestock and agribusiness	183,984		279,173
Municipal lease finance receivables	74,691		77,834
Consumer and other loans	71,176		69,884
Total gross loans, excluding PCI loans	3,687,681		3,699,267
Less: Deferred loan fees, net	(8,528)		(8,567)
Gross loans, excluding PCI loans, net of deferred loan fees	3,679,153		3,690,700
Less: Allowance for loan losses	(59,554)		(59,825)
Net PCI loans	3,619,599		3,630,875
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	13,310		14,605
PCI Loans	110,746		133,496
SBA	440		1,110
Discount on PCI loans	(5,680)		(7,129)
Commercial real estate	93,700		109,350
Construction	0		0
SFR mortgage	203		205
Dairy & livestock and agribusiness	276		4,890
Municipal lease finance receivables	0		0
Consumer and other loans	2,817		3,336
Net PCI loans	$ 105,066		$ 126,367