Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Loans Modified as Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	1	0	3	3
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 278	$ 0	$ 627	$ 5,209
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	278	0	627	5,209
Troubled debt restructurings, Outstanding Recorded Investment	272	0	603	3,297
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial and Industrial [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial and Industrial [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	1	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 38	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	38	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	27	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial Real Estate Owner Occupied [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial Real Estate Owner Occupied [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 3,143
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	3,143
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	3,143
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial Real Estate Non-owner Occupied [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Commercial Real Estate Non-owner Occupied [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
SFR Mortgage [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0
SFR Mortgage [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 311
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	311
Troubled debt restructurings, Outstanding Recorded Investment	0	0	304
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0
Dairy & Livestock and Agribusiness [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Dairy & Livestock and Agribusiness [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 1,984
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	1,984
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	78
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Consumer [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	0	0	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Outstanding Recorded Investment	0	0	0	0
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0
Consumer [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	1	0	1	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment	$ 278	$ 0	$ 278	$ 82
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment	278	0	278	82
Troubled debt restructurings, Outstanding Recorded Investment	272	0	272	76
Troubled debt restructurings, Financial Effect Resulting From Modifications	$ 0	$ 0	$ 0	$ 0