BENEFIT PLANS - 401(K) Employee Stock Ownership Plan (Details) - 401(k) Employee Stock Ownership Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Percentage of first eligible compensation fully matched by employer	3.00%
Percentage of matching contribution in the form of common stock	100.00%
Percentage of the next eligible compensation matched at 50% by employer	3.00%
Percentage of matching contributions for the next eligible compensation in the form of company stock	50.00%
(Income)/expense recognized under plan	$ 6.3	$ 6.1	$ 5.9
Interest credit contribution expense recognized for 401(k) plan	$ 0.9	$ 1.1	$ 0.9
Minimum [Member]
Defined Contribution Plan Disclosure [Line Items]
Contribution from eligible compensation	1.00%
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Contribution from eligible compensation	90.00%