Variable Interest Entities - Royalty Trusts - Open Oil and Natural Gas Commodity Derivative Contracts (Details)	6 Months Ended
Jun. 30, 2014 MBbls
Oil Price Swaps \| July 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	2,054
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	99.08
Oil Price Swaps \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	5,588
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	92.44
Natural Gas Collars \| July 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	472
Collar Range, minimum	4.00
Collar Range, maximum	7.78
Natural Gas Collars \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	1,010
Collar Range, minimum	4.00
Collar Range, maximum	8.55
Royalty Trusts \| Oil Price Swaps \| July 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	823
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	101.01
Royalty Trusts \| Oil Price Swaps \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	904
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	97.78
Royalty Trusts \| Natural Gas Collars \| July 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	472
Collar Range, minimum	4.00
Collar Range, maximum	7.78
Royalty Trusts \| Natural Gas Collars \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	1,010
Collar Range, minimum	4.00
Collar Range, maximum	8.55
Novated Contract \| Royalty Trusts \| Oil Price Swaps \| July 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	473
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	100.76
Novated Contract \| Royalty Trusts \| Oil Price Swaps \| January 2015 - March 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	141
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	100.90

Variable Interest Entities - Royalty Trusts - Open Oil and Natural Gas Commodity Derivative Contracts (Details)

6 Months Ended

Jun. 30, 2014

MBbls

Oil Price Swaps | July 2014 - December 2014

Derivative Instruments and Hedging Activities Disclosure

Notional (Oil in MBbls/Natural Gas in MMcf)

2,054

Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)

99.08

Oil Price Swaps | January 2015 - December 2015

Derivative Instruments and Hedging Activities Disclosure