LOANS AND ALLOWANCE FOR LOAN LOSSES (Narrative) (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) loan	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) agreement	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) loan	Dec. 31, 2015 loan	Dec. 31, 2014	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Unpaid principal balance of loans	$ 24,741,000		$ 24,741,000		$ 17,370,000
Accretable discount on the acquired covered loans	901,000	$ 1,100,000	2,700,000	$ 3,700,000
Total loans	2,141,120,000		2,141,120,000		2,178,961,000
Loans reclassified within portfolio classifications								$ 33,900,000
Accretable discount on acquired EVBS, GAB, PGFSB and HarVest loans	$ 12,400,000		12,400,000		$ 15,100,000
TDRs during period | loan	2				1	1
Mortgage loans on real estate, foreclosures			282,000		$ 282,000
Mortgage loans in process of foreclosure, amount	$ 282,000		282,000		1,500,000
SBA guaranteed amounts included in nonaccrual loans	3,300,000		3,300,000		3,400,000
Mortgage loans trouble debt restructured current amount	651,000		651,000
Doubtful [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	0		0		0
GAB acquisition [Member]
Accounts Notes And Loans Receivable [Line Items]
Loss sharing agreement									$ 143,400,000
Total loans	$ 13,800,000		$ 13,800,000		$ 18,300,000
Federal Deposit Insurance Corporation [Member]
Accounts Notes And Loans Receivable [Line Items]
Number of agreements | agreement			2
Federal Deposit Insurance Corporation [Member] | Single Family Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Term loan agreement expiring			10 years
Federal Deposit Insurance Corporation [Member] | Non Single Family Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term loan agreement expiring							5 years