BUSINESS SEGMENTS AND GEOGRAPHIC INFORMATION - Revenues from External Customers and Long-Lived Assets by Country (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 649,050	$ 687,974	$ 720,868	$ 740,598	$ 696,825	$ 648,872	$ 577,484	$ 564,087	$ 2,798,490	$ 2,487,268	$ 1,804,741
Property, plant and equipment, net	4,502,084				4,857,382				4,502,084	4,857,382	5,001,051
United States
Segment Reporting Information [Line Items]
Operating revenues									2,585,008	2,247,400	1,591,769
Property, plant and equipment, net	4,269,405				4,591,913				4,269,405	4,591,913	4,686,235
Argentina
Segment Reporting Information [Line Items]
Operating revenues									165,718	190,038	157,257
Property, plant and equipment, net	132,321				133,617				132,321	133,617	155,978
Colombia
Segment Reporting Information [Line Items]
Operating revenues									29,757	38,793	37,554
Property, plant and equipment, net	61,757				74,042				61,757	74,042	81,798
Ecuador
Segment Reporting Information [Line Items]
Operating revenues									0	0	6
Property, plant and equipment, net	12				10,781				12	10,781	22,298
Other Foreign
Segment Reporting Information [Line Items]
Operating revenues									18,007	11,037	18,155
Property, plant and equipment, net	$ 38,589				$ 47,029				$ 38,589	$ 47,029	$ 54,742