ACCOUNTING POLICIES (Narrative) (Details) $ in Thousands			3 Months Ended		12 Months Ended
	Apr. 30, 2019 USD ($)	Feb. 01, 2019 USD ($) shares	Mar. 31, 2020 USD ($) item	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies [Line Items]
Number of bank branches | item			149
Number of ATM's | item			170
Impairment charges for goodwill	$ 0		$ 0
Goodwill			935,560		$ 935,560
Loans held for investment, accrued interest receivable			31,100
HTM securities, Accrued interest receivable			5,200
Cash paid in acquisition			$ 0	$ 12
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%
Minimum
Accounting Policies [Line Items]
Intangible assets, amortization period (years)			4 years
Maximum
Accounting Policies [Line Items]
Intangible assets, amortization period (years)			10 years
Access National Bank
Accounting Policies [Line Items]
Number of shares equivalent to each share of acquired entity | shares		0.75
Company's common shares issued | shares		15,842,026
Cash paid in acquisition		$ 12