Loans and the Allowance for Credit Losses - TDRs Defaulted Later Restructured (Detail)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Defaults
Mar. 31, 2017
USD ($)
Defaults
Financing Receivable, Modifications [Line Items]    
Number of Defaults | Defaults 2 1
Recorded Investment | $ $ 129 $ 9
Residential Real Estate [Member]    
Financing Receivable, Modifications [Line Items]    
Number of Defaults | Defaults 1  
Recorded Investment | $ $ 122  
Consumer [Member]    
Financing Receivable, Modifications [Line Items]    
Number of Defaults | Defaults   1
Recorded Investment | $   $ 9
Home Equity [Member]    
Financing Receivable, Modifications [Line Items]    
Number of Defaults | Defaults 1  
Recorded Investment | $ $ 7