Fair Value Measurement and Fair Value of Financial Instruments - Fair Value of Financial Assets Measured on Non-recurring Basis (Detail) - Fair Value, Measurements, Non-recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans and leases	$ 22,591	$ 25,285
Loans held for sale	456	1,742
Other real estate owned and other repossessed assets	843	1,072
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	456	1,742
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans and leases	22,591	25,285
Other real estate owned and other repossessed assets	$ 843	$ 1,072