LONG-TERM DEBT - Summary of Interest Expense Incurred (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Cash Interest, Capitalized Interest	$ (6)	$ (28)	$ (13)	$ (93)
Cash Interest	15,162	15,876	30,172	30,815
Amort. Debt Premium	12	45	24	112
Amort. Debt Issuance Costs & Other Fees	657	950	1,325	2,155
Total Interest Expense	$ 15,831	$ 16,871	$ 31,521	$ 33,082
Senior notes due 2028
Debt Instrument [Line Items]
Effective Interest Rate	6.00%	6.00%	6.00%	6.00%
Cash Interest, Including Amounts Capitalized	$ 14,375	$ 5,566	$ 28,750	$ 5,566
Amort. Debt Premium	12	0	24	0
Amort. Debt Issuance Costs & Other Fees	505	135	1,023	135
Total Interest Expense	14,892	$ 5,701	29,797	$ 5,701
Senior notes due 2022
Debt Instrument [Line Items]
Effective Interest Rate		5.70%		5.70%
Cash Interest, Including Amounts Capitalized	0	$ 8,040	0	$ 21,165
Amort. Debt Premium	0	45	0	112
Amort. Debt Issuance Costs & Other Fees	0	628	0	1,579
Total Interest Expense	0	8,713	0	22,856
Revolver due 2025
Debt Instrument [Line Items]
Cash Interest, Including Amounts Capitalized	287	1,819	416	3,201
Amort. Debt Premium	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	122	165	245	397
Total Interest Expense	$ 409	$ 1,984	$ 661	$ 3,598
Finance lease - real estate
Debt Instrument [Line Items]
Effective Interest Rate	5.90%	6.10%	5.60%	6.00%
Cash Interest, Including Amounts Capitalized	$ 224	$ 52	$ 456	$ 113
Amort. Debt Premium	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	7	7	13	13
Total Interest Expense	231	59	469	126
Non US lines of credit
Debt Instrument [Line Items]
Cash Interest, Including Amounts Capitalized	4	3	7	7
Amort. Debt Premium	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	4	8	8	12
Total Interest Expense	8	11	15	19
Non US term loans
Debt Instrument [Line Items]
Cash Interest, Including Amounts Capitalized	163	292	334	564
Amort. Debt Premium	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	18	7	35	19
Total Interest Expense	181	299	369	583
Other long term debt
Debt Instrument [Line Items]
Cash Interest, Including Amounts Capitalized	115	132	222	292
Amort. Debt Premium	0	0	0	0
Amort. Debt Issuance Costs & Other Fees	1	0	1	0
Total Interest Expense	$ 116	$ 132	$ 223	$ 292

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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