Statements of Consolidated Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Natural gas, tax benefit	$ 28,211	$ 12,984	$ 55,211	$ 27,880
Interest rate, tax expense	25	25	50	50
Pension and other post-retirement benefits liability adjustment, tax expense	$ 128	$ 113	$ 255	$ 227