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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Narrative (Details) - USD ($) shares in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fixed-rate debt | $ 487,148,000 | $ 487,148,000 | $ 500,000,000 |
Investment shares sold (in shares) | 1.6 |  |  |
Proceeds from sale of marketable securities | $ 12,000,000.0 | 11,999,000 | 0 | $ 0
Level 1 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Assets held in a non-qualified supplemental savings plan | 15,700,000 | 15,700,000 | $ 16,200,000 |
MOTIVE Drilling Technologies, Inc. | Recurring Fair Value Measurements | Level 3 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Contingent consideration | 0 | 0 |  |
Carrying Value | Level 2 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fixed-rate debt | $ 487,100,000 | $ 487,100,000 |  |

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