Costs Related to Purchase Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	$ 69,632	$ 57,427	$ 261,619	$ 164,169
Major equipment purchases
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	9,255	6,682	99,416	15,481
486210 Pipeline Transportation of Natural Gas [Member]
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	27,476	24,449	76,839	67,269
Gas drilling obligations
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	$ 32,901	$ 26,296	$ 85,364	$ 81,419