Quarterly report pursuant to Section 13 or 15(d)

SECURITIES (Narrative) (Details)

v3.8.0.1
SECURITIES (Narrative) (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
security
Jun. 30, 2015
USD ($)
Dec. 31, 2017
USD ($)
security
Schedule of Investments [Line Items]      
Individual Available-for-sale securities that had been in a continuous loss position for more than 12 months, amount $ 193,221,000   $ 197,640,000
Available-for-sale securities that had been in a continuous loss position for more than 12 months, unrealized loss 6,477,000   4,188,000
Held to maturity securities unrealized gains before tax 3,200,000 $ 8,100,000 3,600,000
Individual held-to-maturity securities in continuous loss position for more than 12 months $ 2,600,000   $ 1,100,000
Number of held-to-maturity securities in unrealized loss positions | security 4   2
Held-to-maturity securities, continuous unrealized loss position, more than 12 months $ 67,000   $ 31,000
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 $ 42,000,000   $ 27,600,000
Federal Home Loan Bank stock 63,200,000   $ 47,700,000
Credit-related OTTI $ 0    
Available-for-sale Securities      
Schedule of Investments [Line Items]      
Number of available-for-sale securities that had been in a continuous loss position | security 74   71