Loans - Pre-Modification and Post-Modification Outstanding Recorded Investments (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($) contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	106	34
Pre-Modification Outstanding Recorded Investment	$ 102,632	$ 31,354
Post-Modification Outstanding Recorded Investment	$ 95,227	$ 28,872
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	90	19
Pre-Modification Outstanding Recorded Investment	$ 75,894	$ 18,186
Post-Modification Outstanding Recorded Investment	$ 69,020	$ 16,277
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	9	7
Pre-Modification Outstanding Recorded Investment	$ 24,969	$ 11,247
Post-Modification Outstanding Recorded Investment	$ 24,480	$ 10,718
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	6	4
Pre-Modification Outstanding Recorded Investment	$ 23,781	$ 8,325
Post-Modification Outstanding Recorded Investment	$ 23,548	$ 7,092
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	3	3
Pre-Modification Outstanding Recorded Investment	$ 1,188	$ 2,922
Post-Modification Outstanding Recorded Investment	$ 932	$ 3,626
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract	7	7
Pre-Modification Outstanding Recorded Investment	$ 1,769	$ 1,867
Post-Modification Outstanding Recorded Investment	$ 1,727	$ 1,826
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts | contract		1
Pre-Modification Outstanding Recorded Investment		$ 54
Post-Modification Outstanding Recorded Investment		$ 51