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, 2017 Contract	Sep. 30, 2016 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2016 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract	0	2	3	5
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 779	$ 5,209	$ 1,109
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		779	5,209	1,109
Troubled debt restructurings, Outstanding Recorded Investment		773	3,297	1,167
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 0	$ 0	$ 28
Commercial and Industrial [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
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
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 0	$ 0	$ 112
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		0	0	112
Troubled debt restructurings, Outstanding Recorded Investment		0	0	184
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 0	$ 0	$ 0
Small Business Administration [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
Small Business Administration [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract		1	0	2
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 20	$ 0	$ 214
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		20	0	214
Troubled debt restructurings, Outstanding Recorded Investment		14	0	202
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 0	$ 0	$ 28
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
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
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	1	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 0	$ 3,143	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		0	3,143	0
Troubled debt restructurings, Outstanding Recorded Investment		0	3,143	0
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 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
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
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		1	0	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 759	$ 0	$ 759
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		759	0	759
Troubled debt restructurings, Outstanding Recorded Investment		759	0	759
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
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
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	1	0
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 0	$ 1,984	$ 0
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		0	1,984	0
Troubled debt restructurings, Outstanding Recorded Investment		0	78	0
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 0	$ 0	$ 0
Consumer [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
Consumer [Member] | Change in Amortization Period or Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, Number of Loans | Contract		0	1	1
Troubled debt restructurings, Pre-Modification Outstanding Recorded Investment		$ 0	$ 82	$ 24
Troubled debt restructurings, Post-Modification Outstanding Recorded Investment		0	82	24
Troubled debt restructurings, Outstanding Recorded Investment		0	76	22
Troubled debt restructurings, Financial Effect Resulting From Modifications		$ 0	$ 0	$ 0