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 ($)	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 13,769,000
Total Past Due and Accruing		$ 1,653,000
Nonaccrual	11,775,000	5,277,000
Loans Not Past Due	8,394,103,000
Loans Not Past Due and accruing		7,561,389,000
Nonaccrual with No Allowance for Credit Losses	8,785,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	8,407,872,000	7,568,319,000
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,118,000
Total Past Due and Accruing		878,000
Nonaccrual	571,000	59,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,328,000
Total Past Due and Accruing		775,000
Nonaccrual	2,100,000	1,100,000
Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,323,000
Nonaccrual	7,300,000	2,900,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,351,000
Total Past Due and Accruing		2,000
Nonaccrual	1,822,000	1,266,000
Loans Not Past Due	811,705,000
Loans Not Past Due and accruing		933,859,000
Nonaccrual with No Allowance for Credit Losses	1,421,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	817,056,000	935,127,000
Commercial and Industrial [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,582,000
Total Past Due and Accruing		2,000
Commercial and Industrial [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,209,000	0
Commercial and Industrial [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	560,000
Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,515,000
Total Past Due and Accruing		1,402,000
Nonaccrual	1,724,000	2,032,000
Loans Not Past Due	303,472,000
Loans Not Past Due and accruing		301,574,000
Nonaccrual with No Allowance for Credit Losses	850,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	304,987,000	305,008,000
Small Business Administration [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	468,000
Total Past Due and Accruing		870,000
Small Business Administration [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	270,000
Total Past Due and Accruing		532,000
Small Business Administration [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	777,000
SBA - Paycheck Protection Program (PPP) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Nonaccrual	0
Loans Not Past Due	1,101,142,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	1,101,142,000
SBA - Paycheck Protection Program (PPP) [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
SBA - Paycheck Protection Program (PPP) [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	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
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,770,000
Total Past Due and Accruing		0
Nonaccrual	4,766,000	479,000
Loans Not Past Due	2,121,430,000
Loans Not Past Due and accruing		2,083,171,000
Nonaccrual with No Allowance for Credit Losses	4,766,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	2,125,200,000	2,083,650,000
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	0	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	3,770,000
Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,715,000
Total Past Due and Accruing		0
Nonaccrual	1,715,000	245,000
Loans Not Past Due	3,301,308,000
Loans Not Past Due and accruing		3,290,722,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	3,303,023,000	3,290,967,000
Commercial Real Estate Non-owner Occupied [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	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	1,715,000
Construction Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		0
Nonaccrual	0	0
Loans Not Past Due	94,232,000
Loans Not Past Due and accruing		106,895,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	94,232,000	106,895,000
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
Construction Non-speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		0
Nonaccrual	0	0
Loans Not Past Due	7,671,000
Loans Not Past Due and accruing		10,030,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	7,671,000	10,030,000
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
SFR Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	467,000
Total Past Due and Accruing		249,000
Nonaccrual	675,000	878,000
Loans Not Past Due	274,264,000
Loans Not Past Due and accruing		282,341,000
Nonaccrual with No Allowance for Credit Losses	675,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	274,731,000	283,468,000
SFR Mortgage [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		6,000
SFR Mortgage [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		243,000
SFR Mortgage [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	467,000
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	849,000
Total Past Due and Accruing		0
Nonaccrual	849,000	0
Loans Not Past Due	251,953,000
Loans Not Past Due and accruing		383,709,000
Nonaccrual with No Allowance for Credit Losses	849,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	252,802,000	383,709,000
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	849,000	0
Dairy & Livestock and Agribusiness [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Municipal Lease Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		0
Nonaccrual	0	0
Loans Not Past Due	38,040,000
Loans Not Past Due and accruing		53,146,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	38,040,000	53,146,000
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
Consumer and Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	102,000
Total Past Due and Accruing		0
Nonaccrual	224,000	377,000
Loans Not Past Due	88,886,000
Loans Not Past Due and accruing		115,942,000
Nonaccrual with No Allowance for Credit Losses	224,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	88,988,000	116,319,000
Consumer and Other Loans [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	68,000	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	$ 34,000

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 ($)