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 ($)	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 8,318,000
Total Past Due and Accruing		$ 1,653,000
Nonaccrual	6,792,000	5,277,000
Loans Not Past Due	8,394,216,000
Loans Not Past Due and accruing		7,561,389,000
Nonaccrual with No Allowance for Credit Losses	3,837,000
Loans Past Due Over 89 Days Still Accruing	25,000
Total loans	8,402,534,000	7,568,319,000
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,925,000
Total Past Due and Accruing		878,000
Nonaccrual		59,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	930,000
Total Past Due and Accruing		775,000
Nonaccrual	267,000	1,100,000
Greater than 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,463,000
Nonaccrual	5,500,000	2,900,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,852,000
Total Past Due and Accruing		2,000
Nonaccrual	1,197,000	1,266,000
Loans Not Past Due	838,886,000
Loans Not Past Due and accruing		933,859,000
Nonaccrual with No Allowance for Credit Losses	567,000
Loans Past Due Over 89 Days Still Accruing	25,000
Total loans	840,738,000	935,127,000
Commercial and Industrial [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	630,000
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	218,000
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	1,004,000
Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,802,000
Total Past Due and Accruing		1,402,000
Nonaccrual	1,598,000	2,032,000
Loans Not Past Due	298,354,000
Loans Not Past Due and accruing		301,574,000
Nonaccrual with No Allowance for Credit Losses	1,140,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	300,156,000	305,008,000
Small Business Administration [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
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	214,000
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	1,588,000
SBA - Paycheck Protection Program (PPP) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Nonaccrual	0
Loans Not Past Due	1,097,150,000
Nonaccrual with No Allowance for Credit Losses	0
Loans Past Due Over 89 Days Still Accruing	0
Total loans	1,097,150,000
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	232,000
Total Past Due and Accruing		0
Nonaccrual	684,000	479,000
Loans Not Past Due	2,074,233,000
Loans Not Past Due and accruing		2,083,171,000
Nonaccrual with No Allowance for Credit Losses	534,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	2,074,465,000	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
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	0
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	232,000
Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,719,000
Total Past Due and Accruing		0
Nonaccrual	1,944,000	245,000
Loans Not Past Due	3,288,936,000
Loans Not Past Due and accruing		3,290,722,000
Nonaccrual with No Allowance for Credit Losses	228,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	3,290,655,000	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	4,000
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	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	111,222,000
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	111,222,000	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	14,593,000
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	14,593,000	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	1,150,000
Total Past Due and Accruing		249,000
Nonaccrual	1,080,000	878,000
Loans Not Past Due	285,376,000
Loans Not Past Due and accruing		282,341,000
Nonaccrual with No Allowance for Credit Losses	1,079,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	286,526,000	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	446,000
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	704,000
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	882,000
Total Past Due and Accruing		0
Nonaccrual	0	0
Loans Not Past Due	250,939,000
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 loans	251,821,000	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	882,000
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	49,876,000
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	49,876,000	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	681,000
Total Past Due and Accruing		0
Nonaccrual	289,000	377,000
Loans Not Past Due	84,651,000
Loans Not Past Due and accruing		115,942,000
Nonaccrual with No Allowance for Credit Losses	289,000
Loans Past Due Over 89 Days Still Accruing	0
Total loans	85,332,000	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	409,000
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	52,000
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	$ 220,000

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 ($)