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 Type of Loans (Detail) - Loans, Excluding PCI Loans [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	$ 318	$ 1,681
Nonaccrual	23,648	32,186
Current	3,712,410	3,665,400
Total gross loans, excluding PCI loans	3,736,376	3,699,267
30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	318	1,543
60 - 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	138
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	978
Nonaccrual	1,051	2,308
Current	412,658	386,725
Total gross loans, excluding PCI loans	413,709	390,011
Commercial and Industrial [Member] \| 30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	943
Commercial and Industrial [Member] \| 60 - 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	35
Small Business Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	75
Nonaccrual	2,634	2,481
Current	113,492	131,709
Total gross loans, excluding PCI loans	116,126	134,265
Small Business Administration [Member] \| 30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	75
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
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	122
Nonaccrual	4,279	4,072
Current	818,540	786,173
Total gross loans, excluding PCI loans	822,819	790,367
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	36
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	86
Commercial Real Estate Non-owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	266	0
Nonaccrual	12,417	19,246
Current	1,733,626	1,678,190
Total gross loans, excluding PCI loans	1,746,309	1,697,436
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	266	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 and Accruing	0	0
Construction Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	0
Current	42,915	36,574
Total gross loans, excluding PCI loans	42,915	36,574
Construction Speculative [Member] \| 30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Construction Speculative [Member] \| 60 - 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Construction Non-speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	0
Current	14,663	18,599
Total gross loans, excluding PCI loans	14,663	18,599
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
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
SFR Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	425
Nonaccrual	2,778	3,240
Current	218,918	201,459
Total gross loans, excluding PCI loans	221,696	205,124
SFR Mortgage [Member] \| 30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	425
SFR Mortgage [Member] \| 60 - 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Dairy & Livestock and Agribusiness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	103
Current	212,670	279,070
Total gross loans, excluding PCI loans	212,670	279,173
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
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
Municipal Lease Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	0	0
Nonaccrual	0	0
Current	75,839	77,834
Total gross loans, excluding PCI loans	75,839	77,834
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
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
Consumer and Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	52	81
Nonaccrual	489	736
Current	69,089	69,067
Total gross loans, excluding PCI loans	69,630	69,884
Consumer and Other Loans [Member] \| 30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due and Accruing	52	64
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	$ 17

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 Type of Loans (Detail) - Loans, Excluding PCI Loans [Member] - USD ($)
$ in Thousands

Sep. 30, 2015

Dec. 31, 2014

Accounts, Notes, Loans and Financing Receivable [Line Items]