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Concentration of Risk and Off-Balance Sheet Risk (Narrative) (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Concentration Risk [Line Items]    
Commitments to extend credit $ 201,749,000 $ 157,338,000
Balance of loans sold under the program $ 9,206,000 5,958,000
Concentration risk, benchmark description 10% or more of the Bank's total net loans outstanding  
Benchmark - Loans Receivable, Net [Member]    
Concentration Risk [Line Items]    
Concentration risk, percentage 48.80%  
Financial Standby Letters of Credit [Member]    
Concentration Risk [Line Items]    
Commitments to extend credit $ 14,000,000 $ 15,805,000