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Investment Securities (Narrative) (Detail)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
USD ($)
Security
Jun. 30, 2017
USD ($)
Security
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Security
Dec. 31, 2015
USD ($)
Security
Dec. 31, 2014
USD ($)
Schedule of Investments [Line Items]            
Available-for-sale Securities Pledged as Collateral $ 126,032,000 $ 126,032,000   $ 131,469,000 $ 130,298,000  
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | Security 97 97   151 47  
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 1,719,000 $ 1,719,000   $ 4,565,000 $ 403,000  
Available-for-sale, Securities in Unrealized Loss Positions, Depreciation Percentage       3.82% 1.19%  
Available-for-sale Securities, Gross Realized Gains 77,000 200,000 $ 450,000 $ 1,927,000 $ 325,000 $ 168,000
Available-for-sale Securities, Gross Realized Losses (65,000) (180,000) $ (237,000) $ 881,000 0 $ 0
Number of debt securities sold for gross realized gains | Security       102    
Number of debt securities sold for gross realized losses | Security       56    
Held to maturity securities $ 71,096,000 $ 71,096,000   $ 0 $ 0  
Debt Securities [Member]            
Schedule of Investments [Line Items]            
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | Security       149 45  
Equity Securities [Member]            
Schedule of Investments [Line Items]            
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | Security 1 1   2 2  
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 40,000 $ 40,000   $ 112,000 $ 33,000