Quarterly report pursuant to Section 13 or 15(d)

SECURITIES (Narrative) (Details)

v3.8.0.1
SECURITIES (Narrative) (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
security
Jun. 30, 2015
USD ($)
Sep. 30, 2017
USD ($)
security
Dec. 31, 2016
USD ($)
security
Dec. 31, 2015
USD ($)
Schedule of Investments [Line Items]          
Individual securities that had been in a continuous loss position for more than 12 months, amount $ 84,493,000   $ 84,493,000 $ 83,152,000  
Securities that had been in a continuous loss position for more than 12 months, unrealized loss 1,666,000   1,666,000 1,790,000  
Held to maturity securities unrealized gains before tax   $ 8,100,000 4,000,000 5,200,000  
Held-to-maturity securities in continuous loss position for more than 12 months $ 638,000   $ 638,000 $ 648,000  
Number of held-to-maturity securities in unrealized loss positions | security 1   1 1  
Held-to-maturity securities, continuous unrealized loss position, more than 12 months $ 24,000   $ 24,000 $ 81,000  
Federal Home Loan Bank requires Bank to maintain percentage of stock equal to outstanding borrowings     4.25% 4.25%  
Percentage of Federal Reserve Bank of Richmond reserve     6.00% 6.00%  
Restricted equity securities consist of Federal Reserve Bank stock 27,600,000   $ 27,600,000 $ 23,800,000  
Federal Home Loan Bank stock 40,900,000   40,900,000 $ 37,000,000  
Credit-related OTTI $ 0   $ 0   $ 300,000
Available-for-sale Securities          
Schedule of Investments [Line Items]          
Individual securities that had been in a continuous loss position | security 36   36 30