LONG-TERM DEBT - Summary of Interest Expense Incurred (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Cash interest, capitalized interest	$ (28)	$ 0	$ (93)	$ 0
Cash interest	15,876	15,906	30,815	31,204
Amort. Debt Discount	45	66	112	134
Amort. Debt Issuance Costs & Other Fees	950	1,545	2,155	2,708
Total Interest Expense	$ 16,871	17,517	$ 33,082	34,046
Senior notes due 2028
Debt Instrument [Line Items]
Effective Interest Rate	6.00%		6.00%
Cash interest, including amounts capitalized	$ 5,566	0	$ 5,566	0
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	135	0	135	0
Total Interest Expense	$ 5,701	$ 0	$ 5,701	$ 0
Senior notes due 2022
Debt Instrument [Line Items]
Effective Interest Rate	5.70%	5.70%	5.60%	5.70%
Cash interest, including amounts capitalized	$ 8,040	$ 13,125	$ 21,165	$ 26,250
Amort. Debt Discount	45	66	112	134
Amort. Debt Issuance Costs & Other Fees	628	951	1,579	1,902
Total Interest Expense	8,713	14,142	22,856	28,286
Revolver due 2025
Debt Instrument [Line Items]
Cash interest, including amounts capitalized	1,819	1,631
Amort. Debt Discount	0	0
Amort. Debt Issuance Costs & Other Fees	165	400
Total Interest Expense	1,984	$ 2,031
Revolver due 2021
Debt Instrument [Line Items]
Cash interest, including amounts capitalized			3,201	2,564
Amort. Debt Discount			0	0
Amort. Debt Issuance Costs & Other Fees			397	541
Total Interest Expense			3,598	$ 3,105
ESOP Loans
Debt Instrument [Line Items]
Effective Interest Rate		7.20%		6.60%
Cash interest, including amounts capitalized	0	$ 449	0	$ 937
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	0	155	0	186
Total Interest Expense	$ 0	$ 604	$ 0	$ 1,123
Capital lease - real estate
Debt Instrument [Line Items]
Effective Interest Rate	6.10%	5.60%	6.00%	5.50%
Cash interest, including amounts capitalized	$ 52	$ 101	$ 113	$ 216
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	7	6	13	12
Total Interest Expense	59	107	126	228
Non US lines of credit
Debt Instrument [Line Items]
Cash interest, including amounts capitalized	3	4	7	11
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	8	4	12	8
Total Interest Expense	11	8	19	19
Non US term loans
Debt Instrument [Line Items]
Cash interest, including amounts capitalized	292	449	564	897
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	7	26	19	53
Total Interest Expense	299	475	583	950
Other long term debt
Debt Instrument [Line Items]
Cash interest, including amounts capitalized	132	147	292	329
Amort. Debt Discount	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	0	3	0	6
Total Interest Expense	$ 132	$ 150	$ 292	$ 335