BUSINESS SEGMENTS AND GEOGRAPHIC INFORMATION - Summary of Financial Information of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 296,171	$ 633,639	$ 542,548	$ 1,248,296
Segment operating income (loss)	(160,923)	(518,541)	(254,146)	(487,173)
North America Solutions
Segment Reporting Information [Line Items]
Revenues	249,939	545,961	451,929	1,070,642
Offshore Gulf of Mexico
Segment Reporting Information [Line Items]
Revenues	29,274	33,079	61,547	73,334
International Solutions
Segment Reporting Information [Line Items]
Revenues	14,813	51,250	25,331	97,712
Other
Segment Reporting Information [Line Items]
Revenues	2,145	3,349	3,741	6,608
Intersegment
Segment Reporting Information [Line Items]
Revenues	(8,680)	(10,649)	(15,802)	(18,545)
Segment operating income (loss)	(3,433)	0	(5,559)	0
Intersegment | North America Solutions
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment | Offshore Gulf of Mexico
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment | International Solutions
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment | Other
Segment Reporting Information [Line Items]
Revenues	(8,680)	(10,649)	(15,802)	(18,545)
Operating Segment
Segment Reporting Information [Line Items]
Revenues	296,171	633,639	542,548	1,248,296
Segment operating income (loss)	(114,819)	(498,079)	(191,377)	(437,578)
Operating Segment | North America Solutions
Segment Reporting Information [Line Items]
Revenues	249,939	545,961	451,929	1,070,642
Segment operating income (loss)	(109,834)	(342,667)	(182,762)	(290,528)
Operating Segment | Offshore Gulf of Mexico
Segment Reporting Information [Line Items]
Revenues	29,274	33,079	61,547	73,334
Segment operating income (loss)	2,978	(3,319)	5,720	3,009
Operating Segment | International Solutions
Segment Reporting Information [Line Items]
Revenues	14,813	51,250	25,331	97,712
Segment operating income (loss)	(3,458)	(152,469)	(11,815)	(149,354)
Operating Segment | Other
Segment Reporting Information [Line Items]
Revenues	10,825	13,998	19,543	25,153
Segment operating income (loss)	$ (1,072)	$ 376	$ 3,039	$ (705)