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, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
PCI Loans	$ 76,022			$ 110,746
Gross loans, excluding PCI loans, net of deferred loan fees	4,237,928		$ 4,016,937
Less: Allowance for loan losses	(60,938)	$ (59,336)	(59,156)	(59,554)	$ (60,709)	$ (59,825)
Total loans and lease finance receivables	4,176,990		3,957,781
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	2,580		7,473
PCI Loans	76,022		93,712	$ 110,746
SBA	348		393
Discount on PCI loans	(2,430)		(3,872)
Commercial real estate	70,589		81,786
Construction	0		0
SFR mortgage	186		193
Dairy & livestock and agribusiness	503		1,429
Municipal lease finance receivables	0		0
Consumer and other loans	1,816		2,438
Less: Allowance for loan losses	(310)	$ 0	0
Net Non-PCI loans	73,282		89,840
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	479,133		434,099
SBA	111,762		106,867
Commercial real estate	2,884,332		2,643,184
Construction	94,009		68,563
SFR mortgage	237,488		233,754
Dairy & livestock and agribusiness	213,830		305,509
Municipal lease finance receivables	71,929		74,135
Consumer and other loans	79,725		69,278
Total gross loans, excluding PCI loans	4,172,208		3,935,389
Less: Deferred loan fees, net	(7,872)		(8,292)
Gross loans, excluding PCI loans, net of deferred loan fees	4,164,336		3,927,097
Less: Allowance for loan losses	(60,628)		(59,156)
Net Non-PCI loans	$ 4,103,708		$ 3,867,941