BUSINESS SEGMENTS AND GEOGRAPHIC INFORMATION - Reconciliation of Segment Operating Income (Loss) to Income from Continuing Operations before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Operating income (loss) from continuing operations	$ (75,430)	$ (57,584)	$ (518,541)	$ 31,368	$ 39,021	$ (167,874)	$ 95,146	$ 54,289	$ (620,187)	$ 20,582	$ 32,964
Gain on sale of assets									46,775	39,691	22,660
Corporate selling, general and administrative costs, corporate depreciation and corporate restructuring charges									167,513	194,416	199,257
Other income (expense)
Interest and dividend income									7,304	9,468	8,017
Interest expense									(24,474)	(25,188)	(24,265)
Gain (loss) on investment securities									(8,720)	(54,488)	1
Gain on sale of subsidiary									14,963	0	0
Other									(5,384)	(1,596)	(876)
Total other income (expense)									(16,311)	(71,804)	(17,123)
Income (loss) from continuing operations before income taxes									(636,498)	(51,222)	15,841
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss) from continuing operations									(544,389)	109,233	140,021
Segment Reconciling Items
Segment Reporting Information [Line Items]
Gain on sale of assets									46,775	39,691	22,660
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Corporate selling, general and administrative costs, corporate depreciation and corporate restructuring charges									$ (122,573)	$ (128,342)	$ (129,717)