Costs Related to Purchase Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	$ 67,124	$ 53,247	$ 191,974	$ 106,336
Major equipment purchases
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	11,474	5,654	90,161	8,747
486210 Pipeline Transportation of Natural Gas [Member]
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	25,424	21,689	49,363	42,821
Gas drilling obligations
Schedule of Costs Related to Purchase Obligations [Line Items]
Total costs related to purchase obligations	$ 30,226	$ 25,904	$ 52,450	$ 54,768