DERIVATIVES - Non-Designated Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivatives
Notional amounts	$ 1,100,000		$ 1,100,000		$ 823,900
Loan Swap Fees	554	$ 1,557	3,105	$ 3,200
Loan customers
Derivatives
Notional amounts	530,500		530,500		411,900
Bank counterparties
Derivatives
Notional amounts	530,500		530,500		411,900
Interest rate swaps | Non-Designated Hedges
Derivatives
Notional amounts	1,061,074		$ 1,061,074		$ 823,894
Weighted average pay rates (as a percent)			2.94%		3.75%
Weighted average receive rates (as a percent)			2.94%		3.75%
Weighted average maturity			10 years 29 days		10 years 9 months 7 days
Fair value of combined interest rate swaps	$ 0		$ 0		$ 0