Royalty Interests (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) a $ / a	Dec. 31, 2020 USD ($)
Net Book Value
Royalty interests acquired	$ 46,266		$ 46,266
Total royalty interests, gross	46,266		46,266
Less: accumulated depletion	(1,115)		(620)
Total royalty interests, net	45,151		$ 45,646
Acquisition of royalty interests	$ 0	$ 16,945
Royalty interest rate	12.50%
1/16th nonparticipating perpetual royalty interests
Real Estate Properties [Line Items]
Nonparticipating perpetual royalty interest rate	6.25%		6.25%
Net Book Value
1/16th nonparticipating perpetual royalty interest	$ 0		$ 0
1/128th nonparticipating perpetual royalty interests
Real Estate Properties [Line Items]
Nonparticipating perpetual royalty interest rate	0.78125%		0.78125%
Net Book Value
1/128th nonparticipating perpetual royalty interest	$ 0		$ 0
Additional real estate acquisitions
Net Book Value
Net royalty interests (acre) | a		1,017
Acquisition of royalty interests		$ 16,900
Average price per net royalty acre acquired (in dollars per acre) | $ / a		16,668