Business Combinations - Narrative (Details) $ / shares in Units, $ in Thousands		3 Months Ended			6 Months Ended
	Feb. 26, 2021 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Sep. 30, 2020 shares
Business Acquisition [Line Items]
Common stock, par value (USD per share) | $ / shares		$ 0.001			$ 0.001
Reverse stock split					83.000
Common stock outstanding post merger (in shares) | shares	17,800,000	17,825,179			17,825,179		0
Transaction costs		$ 2,164		$ 28	$ 3,213	$ 27
Loss on discontinued operations		(18,606)		0	(18,606)	0
Pro Forma
Business Acquisition [Line Items]
Transaction costs		2,200	$ 1,000	$ 3,200	2,200	$ 3,200
Impairment of oil and gas properties			$ 900
Kansas Properties
Business Acquisition [Line Items]
Loss on discontinued operations		18,600			18,600
Riley Exploration
Business Acquisition [Line Items]
Total consideration	$ 26,392
Transaction costs					4,500
Transaction costs, success fees					1,750
Acquisition related costs, paid at closing		300			$ 300
Acquisition related costs, paid at closing, period					30 days
Revenue of acquiree since acquisition date, actual		0			$ 0
Earnings or loss of acquiree since acquisition date, actual		115			115
Riley Exploration | General and Administrative Expense
Business Acquisition [Line Items]
Transaction costs		$ 2,200			$ 3,100
TGC
Business Acquisition [Line Items]
Common stock, par value (USD per share) | $ / shares	$ 0.001
Stock conversion ratio	97.796467
Reverse stock split	0.083