Commitments and Contingencies Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013
Commitments and Contingencies
Estimated Litigation Liability	$ 17.8
Gas gathering and Oil and Gas Through-put Commitments [Member]
Commitments and Contingencies
Long-term Purchase Commitment, Amount	265.8
Office Space Leases [Member]
Commitments and Contingencies
Long-term Purchase Commitment, Amount	$ 12.9

Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.25)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LitigationReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant