Organization and Description of Business Segments (Details) a in Thousands	12 Months Ended
	Dec. 31, 2020 a segment	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of operating segments | segment	2
1/16th nonparticipating perpetual royalty interest
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Nonparticipating perpetual royalty interest rate (in percentage)	6.25%	6.25%
1/128th nonparticipating perpetual royalty interest
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Nonparticipating perpetual royalty interest rate (in percentage)	0.78125%	0.78125%
West Texas
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Area of land (in acres)	880
West Texas | 1/128th Nonparticipating perpetual oil and gas royalty interest
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Area of land (in acres)	85
West Texas | 1/16th Nonparticipating perpetual oil and gas royalty interest
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Area of land (in acres)	371
West Texas | 1/8th Net royalty acres
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Area of land (in acres)	4