SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)		12 Months Ended		58 Months Ended
	Dec. 31, 2005 acquisition	Dec. 31, 2017 USD ($) ATM branch shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2016 USD ($) shares
Number of bank branches | branch		111
Number of ATMs | ATM		180
Number of business acquisitions | acquisition	2
Held for trading securities		$ 0
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%
Number of Days Past Due to Charge Off Real Estate Secured Loans		180 days
Future payments, contractual term		6 months
Goodwill		$ 298,528,000	$ 298,191,000	$ 298,191,000
Impairment charges for goodwill or intangible assets		0
Liabilities for post retirement benefits payable to other beneficiaries		6,300,000	5,900,000	5,900,000
Affordable housing projects, recognized amortization		1,300,000	370,000
Affordable housing projects, tax credits		858,000	882,000
Affordable housing projects, investment amount		11,000,000	9,900,000	9,900,000
Affordable housing projects, liability		$ 7,300,000	$ 7,100,000	$ 7,100,000
Stock options granted | shares		0	0	0
Accruals for uncertain tax positions		$ 0	$ 0	$ 0
Minimum
Commercial loans on nonaccrual status, period		90 days
Period of independent appraisal or valuation		12 months
Period past due to change TDR status		30 days
Estimated useful life of bank premises		3 years
Percentage of fair value of the derivative instruments for the hedge to be highly effective		80.00%
Interest rate lock commitments period		30 days
Tax Position Benefit Recognition Threshold		50.00%
Maximum
Period past due to charge off consumer loans non-real estate secured		120 days
Estimated useful life of bank premises		50 years
Percentage of fair value of the derivative instruments for the hedge to be highly effective		125.00%
Interest rate lock commitments period		120 days
Core Deposits | Minimum
Intangible assets, amortization period		4 years
Core Deposits | Maximum
Intangible assets, amortization period		14 years