Loans and Lease Finance Receivables and Allowance for Credit Losses - Schedule of Recorded Investment in, and Aging of, Past Due and Nonaccrual Loans, Including PCI Loans by Class of Loans (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 13,324,000	$ 15,949,000
Nonaccrual	13,769,000	14,347,000
Loans Not Past Due	8,279,733,000	8,332,859,000
Nonaccrual with No Allowance for Credit Losses	11,713,000	12,556,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	8,293,057,000	8,348,808,000
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,175,000	1,139,000
Nonaccrual		2,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	900,000	3,226,000
Nonaccrual	400,000	1,300,000
Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,249,000	11,584,000
Nonaccrual	11,200,000	11,600,000
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,145,000	7,208,000
Nonaccrual	7,395,000	7,563,000
Loans Not Past Due	2,165,178,000	2,136,051,000
Nonaccrual with No Allowance for Credit Losses	7,395,000	7,563,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	2,172,323,000	2,143,259,000
Commercial Real Estate Owner Occupied [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Real Estate Owner Occupied [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	211,000	0
Commercial Real Estate Owner Occupied [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,934,000	7,208,000
Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	178,000	0
Nonaccrual	0	0
Loans Not Past Due	3,424,280,000	3,358,250,000
Nonaccrual with No Allowance for Credit Losses	0	0
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	3,424,458,000	3,358,250,000
Commercial Real Estate Non-owner Occupied [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	178,000	0
Commercial Real Estate Non-owner Occupied [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Real Estate Non-owner Occupied [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		0
Nonaccrual	0	0
Loans Not Past Due	80,857,000	72,126,000
Nonaccrual with No Allowance for Credit Losses	0	0
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	80,857,000	72,126,000
Construction Speculative [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Speculative [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Speculative [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Non-speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		0
Nonaccrual	0	0
Loans Not Past Due	15,499,000	13,019,000
Nonaccrual with No Allowance for Credit Losses	0	0
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	15,499,000	13,019,000
Construction Non-speculative [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Non-speculative [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction Non-speculative [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,286,000	3,971,000
Nonaccrual	2,412,000	2,273,000
Loans Not Past Due	306,441,000	299,925,000
Nonaccrual with No Allowance for Credit Losses	2,076,000	2,035,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	307,727,000	303,896,000
Small Business Administration [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	258,000	531,000
Small Business Administration [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	2,415,000
Small Business Administration [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,028,000	1,025,000
SBA - Paycheck Protection Program (PPP) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		0
Nonaccrual	0	0
Loans Not Past Due	897,724,000	882,986,000
Nonaccrual with No Allowance for Credit Losses	0	0
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	897,724,000	882,986,000
SBA - Paycheck Protection Program (PPP) [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
SBA - Paycheck Protection Program (PPP) [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
SBA - Paycheck Protection Program (PPP) [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,747,000	3,757,000
Nonaccrual	2,967,000	3,129,000
Loans Not Past Due	749,961,000	808,305,000
Nonaccrual with No Allowance for Credit Losses	1,506,000	1,576,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	753,708,000	812,062,000
Commercial and Industrial [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	452,000	608,000
Commercial and Industrial [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	689,000	811,000
Commercial and Industrial [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,606,000	2,338,000
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	259,000	784,000
Nonaccrual	259,000	785,000
Loans Not Past Due	260,829,000	360,362,000
Nonaccrual with No Allowance for Credit Losses	0	785,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	261,088,000	361,146,000
Dairy & Livestock and Agribusiness [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Dairy & Livestock and Agribusiness [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Dairy & Livestock and Agribusiness [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	259,000	784,000
Municipal Lease Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		0
Nonaccrual	0	0
Loans Not Past Due	42,349,000	45,547,000
Nonaccrual with No Allowance for Credit Losses	0	430,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	42,349,000	45,547,000
Municipal Lease Finance Receivables [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Municipal Lease Finance Receivables [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Municipal Lease Finance Receivables [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
SFR Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	495,000	229,000
Nonaccrual	424,000	430,000
Loans Not Past Due	254,905,000	270,282,000
Nonaccrual with No Allowance for Credit Losses	424,000	0
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	255,400,000	270,511,000
SFR Mortgage [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	266,000	0
SFR Mortgage [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
SFR Mortgage [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	229,000	229,000
Consumer and Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	214,000	0
Nonaccrual	312,000	167,000
Loans Not Past Due	81,710,000	86,006,000
Nonaccrual with No Allowance for Credit Losses	312,000	167,000
Loans Past Due Over 89 Days Still Accruing	0	0
Total loans	81,924,000	86,006,000
Consumer and Other Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	21,000	0
Consumer and Other Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer and Other Loans [Member] | Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 193,000	$ 0