Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Recorded Investment in Loans Held-for-Investment and Related Allowance for Loan Losses by Loan Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	$ 17,308		$ 35,684
Recorded Investment in Loans, Collectively Evaluated for Impairment	4,699,018		4,194,022
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	36,548		73,035
Allowance for Loan Losses, Individually Evaluated for Impairment	88		548
Allowance for Loan Losses, Collectively Evaluated for Impairment	60,112		59,853
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	431		600
PCI Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	0		0
Recorded Investment in Loans, Collectively Evaluated for Impairment	0		0
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	36,548	$ 71,585	73,035
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	0		0
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	431	$ 1,219	600
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	745		1,349
Recorded Investment in Loans, Collectively Evaluated for Impairment	527,914		493,134
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	2		493
Allowance for Loan Losses, Collectively Evaluated for Impairment	8,061		8,973
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Small Business Administration [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	2,273		3,867
Recorded Investment in Loans, Collectively Evaluated for Impairment	121,818		100,176
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	3		33
Allowance for Loan Losses, Collectively Evaluated for Impairment	861		971
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	8,168		15,806
Recorded Investment in Loans, Collectively Evaluated for Impairment	3,324,349		2,895,959
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	40,870		38,808
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	0		7,651
Recorded Investment in Loans, Collectively Evaluated for Impairment	74,148		83,059
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		4
Allowance for Loan Losses, Collectively Evaluated for Impairment	933		1,104
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
SFR Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	4,550		5,502
Recorded Investment in Loans, Collectively Evaluated for Impairment	240,112		235,988
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		6
Allowance for Loan Losses, Collectively Evaluated for Impairment	2,320		2,565
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	829		659
Recorded Investment in Loans, Collectively Evaluated for Impairment	269,653		238,583
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	5,374		5,971
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Municipal Lease Finance Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	0		0
Recorded Investment in Loans, Collectively Evaluated for Impairment	71,352		68,309
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	906		1,033
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	0		0
Consumer and Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment in Loans, Individually Evaluated for Impairment	743		850
Recorded Investment in Loans, Collectively Evaluated for Impairment	69,672		78,814
Recorded Investment in Loans, Acquired with Deteriorated Credit Quality	0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	83		12
Allowance for Loan Losses, Collectively Evaluated for Impairment	787		428
Allowance for Loan Losses, Acquired with Deteriorated Credit Quality	$ 0		$ 0