INCOME TAXES (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amount
Income tax provision at the statutory rate	$ 51.2	$ 47.2	$ 73.2
State income tax expense, net	7.8	8.7	6.4
Non-deductible / non-tax items	0.6	0.4	(0.3)
Effect of enactment of tax reform	0.0	0.6	(7.9)
Adjustments and settlements	0.0	0.0	(0.6)
Other, net	(0.1)	(0.1)	(0.8)
Total Income Tax Expense	$ 59.5	$ 56.8	$ 70.0
Percent
Income tax provision at the statutory rate	21.00%	21.00%	35.00%
State income tax expense, net	3.20%	3.90%	3.00%
Non-deductible / non-tax items	0.20%	0.20%	(0.10%)
Effect of enactment of tax reform	0	0.002	(0.038)
Adjustments and settlements	0.00%	0.00%	(0.30%)
Other, net	0.00%	0.00%	(0.30%)
Income tax provision	24.40%	25.30%	33.50%