CONDENSED CONSOLIDATED STATEMENT OF OPERATIONS (UNAUDITED) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Income Statement [Abstract]
Operating revenues	$ 631,607	$ 573,096	$ 1,378,429	$ 1,332,090
Operating expenses:
Cost of natural gas and other energy	315,575	246,626	741,207	685,635
Operating, maintenance and general	123,858	118,723	244,852	232,608
Depreciation and amortization	59,295	57,559	118,622	112,753
Revenue-related taxes	5,200	4,806	22,567	21,848
Taxes, other than on income and revenues	12,657	13,638	28,127	28,224
Total operating expenses	516,585	441,352	1,155,375	1,081,068
Operating income	115,022	131,744	223,054	251,022
Other income (expenses):
Interest expense	(54,933)	(55,436)	(110,504)	(106,312)
Earnings from unconsolidated investments	25,048	27,542	51,749	46,120
Other, net	224	(352)	366	(63)
Total other expenses, net	(29,661)	(28,246)	(58,389)	(60,255)
Earnings before income taxes	85,361	103,498	164,665	190,767
Federal and state income tax expense	25,588	28,609	44,230	59,418
Net earnings	59,773	74,889	120,435	131,349
Preferred stock dividends	0	(2,170)	0	(4,341)
Loss on extinguishment of preferred stock	0	(3,295)	0	(3,295)
Net earnings available for common stockholders	$ 59,773	$ 69,424	$ 120,435	$ 123,713
Net earnings available for common stockholders per share:
Basic	$ 0.48	$ 0.56	$ 0.97	$ 0.99
Diluted	$ 0.47	$ 0.55	$ 0.96	$ 0.99
Cash dividends declared on common stock per share:	$ 0.15	$ 0.15	$ 0.30	$ 0.30
Weighted average shares outstanding:
Basic	124,712	124,474	124,685	124,445
Diluted	125,875	125,244	125,737	125,202