Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Operating revenues from external customers	$ 194,173	$ 198,850	$ 417,972	$ 436,958
Intersegment revenues	0	0	0	0
Total operating revenues	194,173	198,850	417,972	436,958
Net income (loss)	5,742	8,478	20,620	23,121
Regulated Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers	179,105	178,692	361,106	363,060
Intersegment revenues	109	116	196	216
Total operating revenues	179,214	178,808	361,302	363,276
Net income (loss)	6,127	9,139	17,375	19,520
Regulated Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers	14,830	19,880	56,322	73,363
Intersegment revenues	61	276	264	838
Total operating revenues	14,891	20,156	56,586	74,201
Net income (loss)	(947)	(618)	2,453	3,592
All Other [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers	238	278	544	535
Intersegment revenues	0	0	0	0
Total operating revenues	238	278	544	535
Net income (loss)	562	(43)	792	9
Reconciling Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers	0	0	0	0
Intersegment revenues	(170)	(392)	(460)	(1,054)
Total operating revenues	(170)	(392)	(460)	(1,054)
Net income (loss)	$ 0	$ 0	$ 0	$ 0