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 ($)	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 7,490,278,000
Total Gross loans	7,498,317,000	$ 7,769,439,000
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	661,000	33,000
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	1,700,000	57,000
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	1,427,000	5,290,000
Nonaccrual	6,612,000	19,951,000
Current		7,726,984,000
Total Gross loans	7,498,317,000	7,752,225,000
Loans, Excluding PCI Loans [Member] \| 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	1,124,000	4,431,000
Loans, Excluding PCI Loans [Member] \| 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	303,000	859,000
Loans, Excluding PCI Loans [Member] \| Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	756,000	909,000
Nonaccrual	1,550,000	7,490,000
Current	919,372,000	993,810,000
Total Gross loans	921,678,000	1,002,209,000
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	756,000	820,000
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	0	89,000
Loans, Excluding PCI Loans [Member] \| Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	303,000	1,307,000
Nonaccrual	2,706,000	2,892,000
Current	316,562,000	345,844,000
Total Gross loans	319,571,000	350,043,000
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	0	1,172,000
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	303,000	135,000
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	2,789,000
Nonaccrual	494,000	589,000
Current	2,092,597,000	2,114,612,000
Total Gross loans	2,093,091,000	2,117,990,000
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	2,439,000
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	350,000
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	368,000	0
Nonaccrual	589,000	5,479,000
Current	3,281,620,000	3,270,760,000
Total Gross loans	3,282,577,000	3,276,239,000
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	368,000	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	0	0
Current	105,636,000	118,233,000
Total Gross loans	105,636,000	118,233,000
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	14,295,000	4,549,000
Total Gross loans	14,295,000	4,549,000
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	0	285,000
Nonaccrual	888,000	2,937,000
Current	277,756,000	293,282,000
Total Gross loans	278,644,000	296,504,000
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	0	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	285,000
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	0	78,000
Current	311,229,000	393,765,000
Total Gross loans	311,229,000	393,843,000
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	54,468,000	64,186,000
Total Gross loans	54,468,000	64,186,000
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	0	0
Nonaccrual	385,000	486,000
Current	116,743,000	127,943,000
Total Gross loans	117,128,000	128,429,000
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	0	0
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	$ 0	$ 0

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 ($)