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STOCK-BASED COMPENSATION - Summary of Compensation Cost for Stock-Based Payment Arrangements (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense | $ 27,858 | $ 36,329 | $ 34,292
Drilling services operating |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense | 5,927 | 9,086 | 7,132
Research and development |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense | 1,271 | 765 | 328
Selling, general and administrative |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense | 20,660 | 29,960 | 26,832
Restructuring charges |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense | $ 0 | $ (3,482) | $ 0

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