INCOME TAXES (Tax Reform Act) (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Feb. 28, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Impact of Tax Reform Act
Statutory federal rate (as a percent)	21.00%	32.74%	21.00%		35.00%
Reduction of deferred tax liabilities due to Tax Reform Act				$ 2.6	$ 24.5
State tax, low end of range of rate (as a percent)			6.00%
State tax, high end of range of rate (as a percent)			6.50%
Effective tax rate (as a percent)			25.90%	10.70%
Provisional reduction in current income tax expense due Tax Reform Act reflecting use of fiscal year rather than calendar year federal income tax filing				$ 0.1	1.3
Alternative fuel tax credit					$ 1.2