Variable Interest Entities - Royalty Trusts - Open Oil and Natural Gas Commodity Derivative Contracts (Details)	Jun. 30, 2013 MBbls
Oil Price Swaps \| July 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	6,211
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	99.19
Oil Price Swaps \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	7,511
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	92.42
Oil Price Swaps \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	5,076
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	83.69
Natural Gas Collars \| July 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	3,432
Collar Range, minimum	3.78
Collar Range, maximum	6.71
Natural Gas Collars \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	937
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 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	803
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	103.04
Royalty Trusts \| Oil Price Swaps \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	1,862
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	100.70
Royalty Trusts \| Oil Price Swaps \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	630
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	101.03
Royalty Trusts \| Oil Price Swaps \| Novated Contract \| July 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	627
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	103.27
Royalty Trusts \| Oil Price Swaps \| Novated Contract \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	991
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	100.79
Royalty Trusts \| Oil Price Swaps \| Novated Contract \| 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
Royalty Trusts \| Natural Gas Collars \| July 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	432
Collar Range, minimum	4.00
Collar Range, maximum	7.15
Royalty Trusts \| Natural Gas Collars \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure
Notional (Oil in MBbls/Natural Gas in MMcf)	937
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

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

Jun. 30, 2013

MBbls

Oil Price Swaps | July 2013 - December 2013

Derivative Instruments and Hedging Activities Disclosure

Notional (Oil in MBbls/Natural Gas in MMcf)

6,211

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

99.19

Oil Price Swaps | January 2014 - December 2014

Derivative Instruments and Hedging Activities Disclosure

Notional (Oil in MBbls/Natural Gas in MMcf)