Investments In Unconsolidated Affiliates (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Schedule of Equity Method Investments (Textuals) [Abstract]
Share of the equity in earnings from unconsolidated affiliates	$ 1,306,000	$ (23,632,000)	$ 3,008,000	$ (21,837,000)
Capital contribution during the period			65,027,000	1,538,000
Investments in unconsolidated affiliates (Textuals) [Abstract]
Distributions related to other equity investments			1,208,000	2,122,000
Bighorn [Member]
Schedule of Equity Method Investments (Textuals) [Abstract]
Investment	337,592,000		337,592,000
Share of the equity in earnings from unconsolidated affiliates			(1,825,000)	(26,930,000)
Capital contribution during the period			432,000	630,000
Fort Union Gas Gathering [Member]
Schedule of Equity Method Investments (Textuals) [Abstract]
Condition for distribute cash to members			only if its ratio of net operating cash flow to debt service is not less than 1.25 to 1.00 and it is not otherwise in default under its credit agreement.
Share of the equity in earnings from unconsolidated affiliates			3,659,000	3,544,000
Other Unconsolidated Investments [Member]
Schedule of Equity Method Investments (Textuals) [Abstract]
Share of the equity in earnings from unconsolidated affiliates			1,173,000	1,549,000
Capital contribution during the period			62,157,000	0
Fort Union [Member]
Schedule of Equity Method Investments (Textuals) [Abstract]
Investment	214,696,000		214,696,000
Capital contribution during the period			$ 0	$ 774,000