BORROWINGS (Narrative) (Details) - USD ($) $ in Thousands				12 Months Ended
	Aug. 29, 2019	Feb. 01, 2019	Aug. 23, 2012	Dec. 31, 2020	Nov. 30, 2020	Dec. 31, 2019
Subordinated Borrowing [Line Items]
Remaining available balance for the federal funds lines				$ 847,000		$ 682,000
Maximum collateral dependent line of credit with the FHLB				6,000,000		5,200,000
Subordinated debt redeemed					$ 8,500
Prepayment of long-term FHLB advances				550,000
FHLB advances, prepayment penalty	$ 7,400		$ 19,600	31,200
Remaining borrowing capacity				25,000		25,000
Trust Preferred Capital Notes
Subordinated Borrowing [Line Items]
Remaining fair value discount on acquired notes				14,100		14,900
Long-term debt borrowings				155,159
Subordinated Debt
Subordinated Borrowing [Line Items]
Remaining fair value discount on acquired notes				1,200		$ 1,400
Long-term debt borrowings				150,000
StellarOne Bank and Xenith | Trust Preferred Capital Notes
Subordinated Borrowing [Line Items]
Trust preferred capital notes principal balance				58,500
Trust preferred securities acquired				$ 87,000
Access National Bank
Subordinated Borrowing [Line Items]
Trust preferred securities acquired		$ 5,000