Summary of Significant Accounting Policies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Significant Accounting Policies [Abstract]
Parent, total ownership percentage	70.00%
Parent, limited partner ownership percentage	68.00%
Parent, general partner ownership percentage	2.00%
Prior Period
Prior Period Reclassification Adjustment		$ 10,400,000	$ 9,400,000
BusinessAcquisitionPurchasePriceAllocationPropertyPlantAndEquipmentAbstract
BusinessAcquisitionPurchasePriceAllocationPropertyPlantAndEquipment	1,500,000,000
Purchase price straight-line depreciation number of years	40
Purchase Price approximate annual depreciation amount	36,000,000
Schedule of Equity Method Investments [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions	14,300,000	6,200,000	8,400,000
Return of capital from unconsolidated affiliates	11,327,000	1,925,000	0
Contributions to unconsolidated affiliates	(5,806,000)	(14,834,000)	0
Nonoperating Income (Expense) [Abstract]
PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest	6,000,000	4,700,000	3,800,000
PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	13,200,000	10,600,000	8,500,000
Cardinal Pipeline Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	45.00%
Return of capital from unconsolidated affiliates	11,300,000
Contributions to unconsolidated affiliates	(5,800,000)	(14,800,000)
Pine Needle LNG Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	35.00%
Return of capital from unconsolidated affiliates		1,900,000
Gathering Facilities | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	0.18%	0.18%	0.18%
Gathering Facilities | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	1.66%	1.66%	1.66%
Storage Facilities | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	2.10%	2.10%	2.10%
Storage Facilities | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	3.70%	3.70%	3.70%
Onshore Transmission Facilities | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	2.79%	2.79%	2.79%
Onshore Transmission Facilities | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	5.71%	5.71%	5.71%
Offshore Transmission Facilities | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	1.01%	1.01%	1.01%
Offshore Transmission Facilities | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Straight-Line Depreciation Rates	1.01%	1.01%	1.01%
Remaining Purchase Price Allocation
BusinessAcquisitionPurchasePriceAllocationPropertyPlantAndEquipmentAbstract
BusinessAcquisitionPurchasePriceAllocationPropertyPlantAndEquipment	$ 800,000,000