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Litigation (Details) - USD ($) | Jun. 30, 2015 | Mar. 12, 2015 | Dec. 31, 2014 | Jun. 30, 2014 | Aug. 31, 2011 | Oct. 31, 2010
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Loss Contingencies [Line Items] |  |  |  |  |  |
Potential liabilities related to litigation and environmental matters | $ 20,700,000 |  | $ 27,600,000 | $ 32,100,000 |  |
Natural gas gathering operations [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Arbitration award |  |  |  |  |  | $ 26,600,000
Litigation related to construction materials [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Loss contingency, estimate of possible loss |  |  |  |  | $ 3,700,000 |
Additional amount per day of potential penalties |  |  |  |  | $ 5,000 |
Litigation related to construction services [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Damage Repair Estimate |  | $ 26,000,000 |  |  |  |

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