Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 segment	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information
Number of business segments	2
Segment Reporting Information, Profit (Loss)
Operating revenues from continuing operations	$ 320,406	$ 276,429	$ 1,265,917	$ 1,126,522
Operating income (loss) from continuing operations	(4,052)	13,964	240,571	350,305
Other income (expense)	(5,061)	(15,791)	(36,804)	(45,074)
Income (Loss) From Continuing Operations Before Income Taxes	(9,113)	(1,827)	203,767	305,231
Identifiable assets	6,614,872		6,614,872		6,175,890
Oil and gas operations
Segment Reporting Information, Profit (Loss)
Operating revenues from continuing operations	272,038	214,620	875,350	799,339
Operating income (loss) from continuing operations	18,607	26,913	181,948	280,897
Other income (expense)	(13,209)	(12,703)	(38,686)	(35,402)
Identifiable assets	5,444,672		5,444,672		4,975,170
Natural gas distribution
Segment Reporting Information, Profit (Loss)
Operating revenues from continuing operations	48,368	61,809	390,567	327,183
Operating income (loss) from continuing operations	(22,544)	(12,743)	58,968	70,265
Other income (expense)	7,973	(3,274)	1,477	(10,062)
Identifiable assets	1,127,487		1,127,487		1,177,134
Eliminations and corporate expenses
Segment Reporting Information, Profit (Loss)
Operating income (loss) from continuing operations	(115)	(206)	(345)	(857)
Other income (expense)	175	186	405	390
Identifiable assets	$ 42,713		$ 42,713		$ 23,586