SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - International Land Drilling Risks (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) item	Mar. 31, 2018 USD ($)
Risk or uncertainty
Cumulative inflation rate before a country is considered highly inflationary (as a percent)			100.00%
Period for which cumulative inflation rates used for considering country as highly inflationary			3 years
Foreign currency loss (gain) | $	$ 0.7	$ (0.2)	$ 4.6	$ 1.4
Minimum
Risk or uncertainty
Number Of Geographical Areas Of Operation To Minimize Risks | item			1