Intangible Assets (Details) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Mar. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Details of Intangible Assets
Weighted Average Remaining Amortization Period			16 years	18 years
Gross Carrying Amount			$ 224,910,000	$ 258,878,000
Accumulated Amortization			(63,258,000)	(66,453,000)
Net			161,652,000	192,425,000
Rights-of-way and easements
Details of Intangible Assets
Weighted Average Remaining Amortization Period			19 years	19 years
Gross Carrying Amount			151,329,000	145,598,000
Accumulated Amortization			(32,605,000)	(28,822,000)
Net			118,724,000	116,776,000
Contracts
Details of Intangible Assets
Weighted Average Remaining Amortization Period			10 years	17 years
Gross Carrying Amount			68,717,000	108,416,000
Accumulated Amortization			(28,802,000)	(36,014,000)
Net			39,915,000	72,402,000
Non-cash impairment charge	5,000,000	28,744,000
Customer relationships
Details of Intangible Assets
Weighted Average Remaining Amortization Period			10 years	11 years
Gross Carrying Amount			4,864,000	4,864,000
Accumulated Amortization			(1,851,000)	(1,617,000)
Net			$ 3,013,000	$ 3,247,000