Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Recorded Investment in, and Aging of, Past Due and Nonaccrual Loans, Excluding PCI Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	$ 1,400	$ 514
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	423	435
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	829
Loans, Excluding PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	271	436
Nonaccrual	11,573	7,152
Current	4,704,482	4,322,843
Total gross loans, excluding PCI loans	4,716,326	4,330,431
Loans, Excluding PCI Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	271	436
Loans, Excluding PCI Loans [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] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	45	0
Nonaccrual	313	156
Current	528,301	484,922
Total gross loans, excluding PCI loans	528,659	485,078
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	45	0
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	0
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	352
Nonaccrual	1,611	2,737
Current	122,480	94,095
Total gross loans, excluding PCI loans	124,091	97,184
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	352
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	0	0
Loans, Excluding PCI Loans [Member] | Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	220	0
Nonaccrual	4,184	635
Current	1,065,953	949,184
Total gross loans, excluding PCI loans	1,070,357	949,819
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	220	0
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	0
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	0	0
Nonaccrual	2,544	1,048
Current	2,259,616	1,979,274
Total gross loans, excluding PCI loans	2,262,160	1,980,322
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	0	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	54,562	48,841
Total gross loans, excluding PCI loans	54,562	48,841
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	19,586	37,038
Total gross loans, excluding PCI loans	19,586	37,038
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	0
Nonaccrual	1,349	2,207
Current	243,313	248,398
Total gross loans, excluding PCI loans	244,662	250,605
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	0
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	829	0
Current	269,653	338,631
Total gross loans, excluding PCI loans	270,482	338,631
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	71,352	64,639
Total gross loans, excluding PCI loans	71,352	64,639
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	6	84
Nonaccrual	743	369
Current	69,666	77,821
Total gross loans, excluding PCI loans	70,415	78,274
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	6	84
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