Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Loan, Excluding PCI Loans by Internal Risk Ratings (Detail) - Loans, Excluding PCI Loans [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 528,659	$ 485,078
SBA	124,091	97,184
Commercial real estate, Owner occupied	1,070,357	949,819
Commercial real estate, Non-owner occupied	2,262,160	1,980,322
Construction, Speculative	54,562	48,841
Construction, Non-speculative	19,586	37,038
SFR mortgage	244,662	250,605
Dairy & livestock and agribusiness	270,482	338,631
Municipal lease finance receivables	71,352	64,639
Consumer and other loans	70,415	78,274
Total gross loans, excluding PCI loans	4,716,326	4,330,431
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	485,025	449,658
SBA	113,423	80,138
Commercial real estate, Owner occupied	960,523	842,992
Commercial real estate, Non-owner occupied	2,238,827	1,941,203
Construction, Speculative	51,596	48,841
Construction, Non-speculative	19,586	37,038
SFR mortgage	236,027	243,374
Dairy & livestock and agribusiness	206,720	187,819
Municipal lease finance receivables	70,723	60,102
Consumer and other loans	67,362	74,328
Total gross loans, excluding PCI loans	4,449,812	3,965,493
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	30,675	21,610
SBA	4,504	10,553
Commercial real estate, Owner occupied	88,507	87,781
Commercial real estate, Non-owner occupied	16,363	23,534
Construction, Speculative	2,966	0
Construction, Non-speculative	0	0
SFR mortgage	4,560	4,930
Dairy & livestock and agribusiness	46,614	114,106
Municipal lease finance receivables	629	4,537
Consumer and other loans	1,457	2,123
Total gross loans, excluding PCI loans	196,275	269,174
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	12,959	13,809
SBA	6,164	6,482
Commercial real estate, Owner occupied	21,327	19,046
Commercial real estate, Non-owner occupied	6,970	15,585
Construction, Speculative	0	0
Construction, Non-speculative	0	0
SFR mortgage	4,075	2,301
Dairy & livestock and agribusiness	17,148	36,706
Municipal lease finance receivables	0	0
Consumer and other loans	1,594	1,819
Total gross loans, excluding PCI loans	70,237	95,748
Doubtful & Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	0	1
SBA	0	11
Commercial real estate, Owner occupied	0	0
Commercial real estate, Non-owner occupied	0	0
Construction, Speculative	0	0
Construction, Non-speculative	0	0
SFR mortgage	0	0
Dairy & livestock and agribusiness	0	0
Municipal lease finance receivables	0	0
Consumer and other loans	2	4
Total gross loans, excluding PCI loans	$ 2	$ 16