FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Narrative (Details) - USD ($)	3 Months Ended
Dec. 31, 2019	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-rate debt	$ 487,148,000	$ 487,148,000
Gain resulting from increases in the fair value of investments	2,800,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held in a non-qualified supplemental savings plan	16,100,000	$ 15,700,000
Level 2 \| Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-rate debt	487,100,000
MOTIVE Drilling Technologies, Inc. \| Level 3 \| Recurring Fair Value Measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ 0

Amount of liability recognized arising from contingent consideration in a business combination.

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Amount of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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