Income Taxes - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 26, 2021	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Provision for deferred income taxes	$ 13,600	$ 12,962	$ 665
Tax Credit Carryforward [Line Items]
Operating loss carryforwards		13,700
Operating loss carryforwards, subject to expiration		4,900
Operating loss carryforwards, not subject to expiration		8,800
Riley Exploration
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, not subject to expiration		$ 12,100