Statements of Condensed Consolidated Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Stockholders' Equity [Abstract]
Natural gas, tax (benefit)	$ 55,211	$ 27,880
Interest rate, tax	50	50
Pension and other post-retirement benefits liability adjustment, tax expense	$ 255	$ 227
Dividends (in dollars per share)	$ 0.06	$ 0.06
Distributions to noncontrolling interests (in dollars per common unit)	$ 1.19	$ 0.95