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Litigation (Details) (USD $) | Mar. 31, 2012 | Dec. 31, 2011 | Mar. 31, 2011 | Mar. 31, 2012 Pending or threatened litigation [Member] Litigation related to construction materials [Member] | Aug. 31, 2011 Pending or threatened litigation [Member] Litigation related to construction materials [Member] | Jan. 18, 2011 Pending or threatened litigation [Member] Litigation related to construction materials [Member] | Mar. 31, 2012 Pending or threatened litigation [Member] Natural gas gathering operations [Member] | Apr. 20, 2011 Pending or threatened litigation [Member] Natural gas gathering operations [Member] | Oct. 31, 2010 Pending or threatened litigation [Member] Natural gas gathering operations [Member] | Sep. 30, 2010 Pending or threatened litigation [Member] Natural gas gathering operations [Member] | Jan. 13, 2012 Pending or threatened litigation [Member] Guarantee obligation under construction contract [Member] | Sep. 19, 2011 Pending or threatened litigation [Member] Guarantee obligation under construction contract [Member] | Dec. 31, 2009 Pending or threatened litigation [Member] Guarantee obligation under construction contract [Member] | Jul. 31, 2007 Pending or threatened litigation [Member] Guarantee obligation under construction contract [Member]
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Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential liabilities related to litigation and environmental matters | $ 70,700,000 | $ 64,100,000 | $ 40,500,000 |  |  |  |  |  |  |  |  |  |  |
Bicent's bank letter of credit guaranteeing CEM's obligation |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,000,000
Amount of compensatory damages in LPP's notice of demand |  |  |  |  |  |  |  |  |  |  |  |  | 149,700,000 |
Amount of counterclaim |  |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |
Arbitration award |  |  |  |  |  |  |  |  | 26,600,000 |  | 22,000,000 |  |  |
Estimated damages in pending litigation, low estimate |  |  |  |  |  | 6,000,000 | 18,800,000 |  |  |  |  |  |  |
Estimated damages in pending litigation, high estimate |  |  |  |  |  | 11,000,000 | 22,600,000 |  |  |  |  |  |  |
Amount of damages dismissed in pending litigation |  |  |  | 5,000,000 |  |  |  |  |  |  |  |  |  |
Estimated damages including interest in amended complaint |  |  |  | 21,900,000 |  |  |  |  |  |  |  |  |  |
Loss contingency, estimate of possible loss |  |  |  |  | 3,700,000 |  |  |  |  |  |  |  |  |
Additional amount per day of potential penalties |  |  |  |  | 5,000 |  |  |  |  |  |  |  |  |
Amount of natural gas gathering contract dispute charged to operations and maintenance, before tax |  |  |  |  |  |  |  |  |  | 26,600,000 |  |  |  |
Amount of natural gas gathering contract dispute charged to operation and maintenance expense, after tax |  |  |  |  |  |  |  |  |  | 16,500,000 |  |  |  |
Legal fees and expenses awarded in litigation |  |  |  |  |  |  |  | $ 293,000 |  |  |  |  |  |

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