Variable Interest Entities - Royalty Trusts - Distributions (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Variable Interest Entity
Distributions to third-party unitholders			$ 84,690	$ 103,142
Royalty Trusts
Variable Interest Entity
Total distributions	$ 47,296	$ 59,672	97,499	127,985
Distributions to third-party unitholders	$ 40,975	$ 50,024	$ 84,690	$ 103,142

Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration