Other Income and Expenses (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Property, plant and equipment additions, net of equity AFUDC*	$ 475,450	$ 385,671	$ 376,502
Component of Operating Other Cost and Expense [Line Items]
Utilities Operating Expense, Maintenance and Operations	292,610	274,735	249,060
Gas Gathering, Transportation, Marketing and Processing Costs	31,815	35,674	32,231
Eminence Storage Field
Component of Operating Other Cost and Expense [Line Items]
Utilities Operating Expense, Maintenance and Operations	2,500	14,600	2,000
Gas Gathering, Transportation, Marketing and Processing Costs			2,500
Rockaway Delivery Lateral Project [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment additions, net of equity AFUDC*	8,700
Northeast Connector Project [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment additions, net of equity AFUDC*	2,400
Northeast Supply Link Expansion Project [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment additions, net of equity AFUDC*		$ 10,100