Loans and Lease Finance Receivables and Allowance for Loan 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, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 9,807,000
Total Past Due and Accruing		$ 1,653,000
Nonaccrual	6,428,000	5,277,000
Loans Not Past Due	7,456,345,000
Loans Not Past Due and accruing		7,561,389,000
Nonaccrual with No Allowance for Credit Losses	4,636,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	7,466,152,000	7,568,319,000
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,196,000
Total Past Due and Accruing		878,000
Nonaccrual	154,000	59,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,626,000
Total Past Due and Accruing		775,000
Nonaccrual	1,300,000	1,100,000
Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,985,000
Nonaccrual	4,000,000.0	2,900,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,196,000
Total Past Due and Accruing		2,000
Nonaccrual	1,703,000	1,266,000
Loans Not Past Due	958,565,000
Loans Not Past Due and accruing		933,859,000
Nonaccrual with No Allowance for Credit Losses	549,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	960,761,000	935,127,000
Commercial and Industrial [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	347,000
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	362,000
Total Past Due and Accruing		0
Commercial and Industrial [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,487,000
Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,709,000
Total Past Due and Accruing		1,402,000
Nonaccrual	2,748,000	2,032,000
Loans Not Past Due	307,362,000
Loans Not Past Due and accruing		301,574,000
Nonaccrual with No Allowance for Credit Losses	2,110,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	313,071,000	305,008,000
Small Business Administration [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,086,000
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	954,000
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	1,669,000
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	714,000
Total Past Due and Accruing		0
Nonaccrual	715,000	479,000
Loans Not Past Due	2,069,646,000
Loans Not Past Due and accruing		2,083,171,000
Nonaccrual with No Allowance for Credit Losses	715,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	2,070,360,000	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	154,000
Total Past Due and Accruing		0
Commercial Real Estate Owner Occupied [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	310,000
Total Past Due and Accruing		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	250,000
Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	210,000
Total Past Due and Accruing		0
Nonaccrual	232,000	245,000
Loans Not Past Due	3,277,355,000
Loans Not Past Due and accruing		3,290,722,000
Nonaccrual with No Allowance for Credit Losses	232,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	3,277,565,000	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	210,000
Total Past Due and Accruing		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
Total Past Due and Accruing		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
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	116,143,000
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 Gross loans	116,143,000	106,895,000
Construction Speculative [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		0
Construction Speculative [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		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	11,902,000
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 Gross loans	11,902,000	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
Total Past Due and Accruing		0
Construction Non-speculative [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		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	719,000
Total Past Due and Accruing		249,000
Nonaccrual	864,000	878,000
Loans Not Past Due	278,024,000
Loans Not Past Due and accruing		282,341,000
Nonaccrual with No Allowance for Credit Losses	864,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	278,743,000	283,468,000
SFR Mortgage [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	233,000
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	486,000
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	166,000
Total Past Due and Accruing		0
Nonaccrual	0	0
Loans Not Past Due	271,948,000
Loans Not Past Due and accruing		383,709,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	272,114,000	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	166,000
Total Past Due and Accruing		0
Dairy & Livestock and Agribusiness [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		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	51,287,000
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 Gross loans	51,287,000	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
Total Past Due and Accruing		0
Municipal Lease Finance Receivables [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		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	93,000
Total Past Due and Accruing		0
Nonaccrual	166,000	377,000
Loans Not Past Due	114,113,000
Loans Not Past Due and accruing		115,942,000
Nonaccrual with No Allowance for Credit Losses	166,000
Loans Past Due Over 89 Days Still Accruing	0
Total Gross loans	114,206,000	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	0
Total Past Due and Accruing		0
Consumer and Other Loans [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Total Past Due and Accruing		$ 0
Consumer and Other Loans [Member] \| Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 93,000

Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Recorded Investment in, and Aging of, Past Due and Nonaccrual Loans, Including PCI Loans by Class of Loans (Detail) - USD ($)