Summary of Significant Accounting Policies - Concentrations and Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Restricted cash	$ 500	$ 500
Value of cost method investment			$ 33,900
Shell Trading [Member] | Customer Concentration Risk [Member] | Royalty Interest Revenue [Member]
Concentration Risk [Line Items]
Percent of total royalty interest revenue	57.00%	68.00%	70.00%
RSP Permian LLC [Member] | Customer Concentration Risk [Member] | Royalty Interest Revenue [Member]
Concentration Risk [Line Items]
Percent of total royalty interest revenue	32.00%	25.00%
Permian Transport & Trading [Member] | Customer Concentration Risk [Member] | Royalty Interest Revenue [Member]
Concentration Risk [Line Items]
Percent of total royalty interest revenue			15.00%
Other assets [Member]
Concentration Risk [Line Items]
Value of cost method investment	$ 33,851