STATEMENTS OF CONSOLIDATED INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating revenues	$ 1,639,934	$ 1,374,395	$ 1,311,356
Operating expenses:
Purchased gas costs	256,467	252,884	360,898
Operation and maintenance	127,642	152,414	140,003
Production	80,911	67,414	62,978
Exploration	4,932	5,368	17,905
Selling, general and administrative	172,294	155,551	176,703
Depreciation, depletion and amortization	339,297	270,285	196,078
Total operating expenses	981,543	903,916	954,565
Gain on dispositions	202,928
Operating income	861,319	470,479	356,791
Other income	34,138	12,898	8,585
Interest expense	136,328	128,157	111,779
Income before income taxes	759,129	355,220	253,597
Income taxes	279,360	127,520	96,668
Net income	$ 479,769	$ 227,700	$ 156,929
Basic:
Net income (in dollars per share)	$ 3.21	$ 1.58	$ 1.20
Diluted:
Net income (in dollars per share)	$ 3.19	$ 1.57	$ 1.19