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Impairment of long-lived assets | 6 Months Ended
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Jun. 30, 2013
Impaired Long-Lived Assets Held and Used [Line Items] |
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] | Impairment of long-lived assets During the second quarters of 2013 and 2012, the Company recognized impairments of coalbed natural gas gathering assets at the pipeline and energy services segment of $14.5 million ($9.0 million after tax) and $2.7 million ($1.7 million after tax), respectively, which are recorded in operation and maintenance expense on the Consolidated Statements of Income. The impairments are related to coalbed natural gas gathering assets located in Wyoming and Montana where there has been a significant decline in natural gas development and production activity largely due to low natural gas prices. The coalbed natural gas gathering assets were written down to fair value that was determined using the income approach. For more information on this nonrecurring fair value measurement see Note 14.

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- Definition Disclosure of accounting policy for recognizing and measuring the impairment of long-lived assets. An entity also may disclose its accounting policy for long-lived assets to be sold. This policy excludes goodwill and intangible assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section CC -Subsection 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2155824 + Details
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