Oil and Natural Gas Properties - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Extractive Industries [Abstract]
Depletion and amortization	$ 6.7	$ 4.8	$ 18.7	$ 15.5