STOCK-BASED COMPENSATION - Summary of Compensation Cost for Stock-Based Payment Arrangements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6,826	$ 10,750	$ 14,277	$ 20,952
Drilling services operating
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,529	2,651	3,292	4,887
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	271	181	607	347
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,026	$ 7,918	$ 10,378	$ 15,718