Annual report pursuant to Section 13 and 15(d)

Royalty Interests (Details)

v3.10.0.1
Royalty Interests (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
a
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
a
Sep. 30, 2017
USD ($)
Jun. 30, 2017
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2018
USD ($)
a
$ / a
Dec. 31, 2017
USD ($)
a
Dec. 31, 2016
USD ($)
Net Book Value                      
Royalty interests acquired $ 24,303       $ 0       $ 24,303 $ 0  
Total royalty interests 24,303       0       $ 24,303 0  
Royalty interests sold (in acres) | a                 812    
Royalty interest rate                 12.50%    
Royalty interests sold 93,201 $ 73,168 $ 73,844 $ 60,007 39,957 $ 51,977 $ 32,293 $ 30,407 $ 300,220 154,634 $ 66,109
Average price per net royalty acre sold (in dollars per acre) | $ / a                 23,234    
Acquisition of royalty interests                 $ 24,303 $ 0 0
1/16th nonparticipating perpetual royalty interest                      
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       $ 0 $ 0  
Gross royalty interests (acre) | a 370,737       373,777       370,737 373,777  
1/128th nonparticipating perpetual royalty interest                      
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       $ 0 $ 0  
Gross royalty interests (acre) | a 84,934       85,414       84,934 85,414  
Acquisition in conjunction with sale of 1/8th interest royalty acres                      
Net Book Value                      
Net royalty interests (acre) | a 1,480               1,480    
Acquisition of royalty interests                 $ 20,600    
Average price per net royalty acre acquired (in dollars per acre) | $ / a                 13,949    
Additional real estate acquisitions                      
Net Book Value                      
Net royalty interests (acre) | a 346               346    
Acquisition of royalty interests                 $ 3,700    
Average price per net royalty acre acquired (in dollars per acre) | $ / a                 10,555    
Sale of oil and gas royalty interests                      
Net Book Value                      
Royalty interests sold                 $ 18,875 $ 0 $ 0