Annual report pursuant to Section 13 and 15(d)

Royalty Interests (Details)

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Royalty Interests (Details)
 3 Months Ended 12 Months Ended
Dec. 31, 2019
USD ($)
a
Sep. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
a
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2019
USD ($)
a
$ / a
Dec. 31, 2018
USD ($)
a
$ / a
$ / shares
Dec. 31, 2017
USD ($)
Net Book Value                      
Royalty interests acquired (3) $ 29,320,000       $ 24,303,000       $ 29,320,000 $ 24,303,000  
Total royalty interests, gross 29,320,000       24,303,000       29,320,000 24,303,000  
Less: accumulated depletion 260,000       0       260,000 0  
Total royalty interests, net 29,060,000       24,303,000       29,060,000 $ 24,303,000  
Royalty interests sold (in acres) | a                   812  
Revenue 113,332,000 $ 98,530,000 $ 87,310,000 $ 191,324,000 93,201,000 $ 73,168,000 $ 73,844,000 $ 60,007,000 490,496,000 $ 300,220,000 $ 154,634,000
Average price per net royalty acre sold (in USD per acre) | $ / a                   23,234  
Acquisition of royalty interests                 5,017,000 $ 24,303,000 0
1/16th nonparticipating perpetual royalty interest                      
Net Book Value                      
1/16th nonparticipating perpetual royalty interest $ 0       $ 0       $ 0 $ 0  
Nonparticipating perpetual royalty interest rate (in percentage)                 6.25% 6.25%  
Gross royalty interests (in acres) | a 370,737       370,737       370,737 370,737  
1/128th nonparticipating perpetual royalty interest                      
Net Book Value                      
1/128th nonparticipating perpetual royalty interest $ 0       $ 0       $ 0 $ 0  
Nonparticipating perpetual royalty interest rate (in percentage)                 0.78125% 0.78125%  
Gross royalty interests (in acres) | a 84,934       84,934       84,934 84,934  
Royalty interests in acres                      
Net Book Value                      
Net royalty interest acquired (in acres) | a 3,074       1,826       3,074 1,826  
Acquisition in conjunction with sale of 1/8th interest royalty acres                      
Net Book Value                      
Net royalty interests (in acres) | a         1,480         1,480  
Acquisition of royalty interests                   $ 20,600,000  
Average price per net royalty acre acquired (in USD per acre) | $ / shares                   13,949  
Additional real estate acquisitions                      
Net Book Value                      
Net royalty interests (in acres) | a 1,247       346       1,247 346  
Acquisition of royalty interests                 $ 4,700,000 $ 3,700,000  
Average price per net royalty acre acquired (in USD per acre) | $ / a                 3,800 10,555  
Sale of oil and gas royalty interests                      
Net Book Value                      
Revenue                 $ 0 $ 18,875,000 $ 0