Fair Value - Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Impaired Loans
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on nonrecurring basis	$ 25,160	$ 26,075
Loans Held For Sale
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on nonrecurring basis		2,143
Level 2 | Loans Held For Sale
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on nonrecurring basis		2,143
Level 3 | Impaired Loans
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on nonrecurring basis	$ 25,160	$ 26,075