LOANS (Loans by credit quality indicator narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Held to maturity	$ 9,854,907,000		$ 9,854,907,000			$ 10,023,051,000
Allowance for credit loss	117,533,000	$ 103,377,000	117,533,000	$ 103,377,000	$ 120,726,000	$ 131,606,000	$ 119,937,000	$ 70,395,000
Loans secured by residential real estate property in process of foreclosure	$ 712,000		$ 712,000
Loans delinquent 30 to 89 days, percentage	0.12%		0.12%			0.23%
Interest income on nonaccrual loans	$ 0	$ 0	$ 0	$ 0
Nonaccrual loans with no related allowance	28,600,000		28,600,000			$ 32,500,000
Nonpass | Paycheck Protection Program ("PPP")
Financing Receivable, Credit Quality Indicator [Line Items]
Held to maturity	52,500,000		52,500,000			$ 77,100,000
Allowance for credit loss	$ 0		$ 0