Other Comprehensive Income Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (23,369)	$ (27,762)	$ (47,041)	$ (57,676)
Revenue	279,826	242,363	660,497	608,214
Income (loss) from continuing operations before earnings (loss) of unconsolidated subsidiaries and income taxes	46,134	(19,919)	110,994	35,125
Income tax benefit (expense)	(15,616)	7,574	(37,193)	(12,143)
Net income (loss) available for common stock	30,518	(13,483)	73,715	16,304
Cash Flow Hedging [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before earnings (loss) of unconsolidated subsidiaries and income taxes	1,848	(1,051)	2,552	(2,238)
Income tax benefit (expense)	(647)	432	(883)	877
Net income (loss) available for common stock	1,201	(619)	1,669	(1,361)
Cash Flow Hedging [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	1,820	1,843	3,616	3,665
Cash Flow Hedging [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Commodity Contract [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Revenue	28	(2,894)	(1,064)	(5,903)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Utilities - Operations and maintenance [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive income, Current Period, before Tax	(31)	0	(62)	0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Non-regulated energy operations and maintenance [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive income, Current Period, before Tax	(32)	0	(64)	0
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Utilities - Operations and maintenance [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive income, Current Period, before Tax	421	0	842	0
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Non-regulated energy operations and maintenance [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive income, Current Period, before Tax	274	0	548	0
Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive income, Current Period, before Tax	632	0	1,264	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax	(268)	0	(443)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 364	$ 0	$ 821	$ 0