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Impairment of long-lived assets	6 Months Ended
Impairment of long-lived assets	Jun. 30, 2014
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	Impairment of long-lived assets During the second quarter of 2013, the Company recognized an impairment of coalbed natural gas gathering assets at the pipeline and energy services segment of $14.5 million ($9.0 million after tax), which is recorded in operation and maintenance expense on the Consolidated Statements of Income. The impairment is 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 15.