INCOME TAXES (Tax Reform Act) (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Impact of Tax Reform Act
Statutory federal rate (as a percent)	32.74%	21.00%		21.00%	21.00%	21.00%	35.00%
Reduction of deferred tax liabilities due to Tax Reform Act			$ 800			$ 3,500	$ 24,500
Tax benefit for change in accumulated other comprehensive income for noncash pension settlement expense		$ 0			$ 0
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)		30.30%	24.50%		28.30%	18.40%
Provisional reduction in current income tax expense due Tax Reform Act reflecting use of fiscal year rather than calendar year federal income tax filing							1,300
Alternative fuel tax credit							$ 1,200
Maximum
Impact of Tax Reform Act
Provisional reduction in current income tax expense due Tax Reform Act reflecting use of fiscal year rather than calendar year federal income tax filing						$ 100