DEPOSITS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deposit Liabilities Disclosures [Line Items]
Interest expense on time deposits of $250,000 or more	$ 7,400,000	$ 7,600,000	$ 8,500,000
Maximum brokered certificates of deposit balance allowed per company policy	450,000,000
Related party deposit liabilities	10,400,000	9,900,000
Demand deposit overdrafts reclassified as loans	933,000	1,700,000
Certificates of deposit - CDs
Deposit Liabilities Disclosures [Line Items]
Brokered certificates of deposit	$ 102,800,000	$ 365,700,000
Brokered certificates of deposit, as a percent of total deposits	2.10%
Weighted average cost, domestic deposit, brokered	0.18%
Brokered certificates of deposit, maturity period, less than	2 years
Category under which brokered certificates of deposit are reported	$ 250,000