Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Recorded Investment in, and Aging of, Past Due and Nonaccrual Loans, Excluding PCI Loans by Class of Loans (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	$ 2,200,000	$ 514,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	81,000	435,000
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	1,300,000
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	1,380,000	436,000
Nonaccrual	10,347,000	7,152,000
Current	4,554,194,000	4,322,843,000
Total gross loans, excluding PCI loans	4,565,921,000	4,330,431,000
Loans, Excluding PCI Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	803,000	436,000
Loans, Excluding PCI Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	577,000	0
Loans, Excluding PCI Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	219,000	0
Nonaccrual	506,000	156,000
Current	528,220,000	484,922,000
Total gross loans, excluding PCI loans	528,945,000	485,078,000
Loans, Excluding PCI Loans [Member] | Commercial and Industrial [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	42,000	0
Loans, Excluding PCI Loans [Member] | Commercial and Industrial [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	177,000	0
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	329,000	352,000
Nonaccrual	1,089,000	2,737,000
Current	111,272,000	94,095,000
Total gross loans, excluding PCI loans	112,690,000	97,184,000
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	328,000	352,000
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	1,000	0
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	2,374,000	635,000
Current	1,045,057,000	949,184,000
Total gross loans, excluding PCI loans	1,047,431,000	949,819,000
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Owner Occupied [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Owner Occupied [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	3,249,000	1,048,000
Current	2,168,619,000	1,979,274,000
Total gross loans, excluding PCI loans	2,171,868,000	1,980,322,000
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Non-owner Occupied [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Non-owner Occupied [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Construction Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	384,000	0
Current	53,305,000	48,841,000
Total gross loans, excluding PCI loans	53,689,000	48,841,000
Loans, Excluding PCI Loans [Member] | Construction Speculative [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Construction Speculative [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Construction Non-speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	0
Current	19,093,000	37,038,000
Total gross loans, excluding PCI loans	19,093,000	37,038,000
Loans, Excluding PCI Loans [Member] | Construction Non-speculative [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Construction Non-speculative [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | SFR Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	403,000	0
Nonaccrual	983,000	2,207,000
Current	243,976,000	248,398,000
Total gross loans, excluding PCI loans	245,362,000	250,605,000
Loans, Excluding PCI Loans [Member] | SFR Mortgage [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	403,000	0
Loans, Excluding PCI Loans [Member] | SFR Mortgage [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	1,324,000	0
Current	242,940,000	338,631,000
Total gross loans, excluding PCI loans	244,264,000	338,631,000
Loans, Excluding PCI Loans [Member] | Dairy & Livestock and Agribusiness [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Dairy & Livestock and Agribusiness [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Municipal Lease Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	0
Current	62,416,000	64,639,000
Total gross loans, excluding PCI loans	62,416,000	64,639,000
Loans, Excluding PCI Loans [Member] | Municipal Lease Finance Receivables [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Municipal Lease Finance Receivables [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Loans, Excluding PCI Loans [Member] | Consumer and Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	429,000	84,000
Nonaccrual	438,000	369,000
Current	79,296,000	77,821,000
Total gross loans, excluding PCI loans	80,163,000	78,274,000
Loans, Excluding PCI Loans [Member] | Consumer and Other Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	30,000	84,000
Loans, Excluding PCI Loans [Member] | Consumer and Other Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	$ 399,000	$ 0