Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Total operating revenues, unaffiliated customers
Total operating revenues, unaffiliated customers	$ 83,897	$ 86,831	$ 204,811	$ 233,429
Intersegment Revenues
Total intersegment revenues	1,444	377	1,957	757
Operating Income
Total operating income	10,455	7,776	30,528	32,615
Other income, net of expenses	153	27	349	50
Interest charges	2,241	2,114	4,532	4,265
Income before income taxes	8,367	5,689	26,345	28,400
Income tax expense	3,307	2,169	10,558	11,133
Net Income	5,060	3,520	15,787	17,267	27,622
Total identifiable assets	679,700		679,700		709,066
Regulated Energy [Member]
Total operating revenues, unaffiliated customers
Total operating revenues, unaffiliated customers	54,330	54,011	126,348	138,695
Intersegment Revenues
Total intersegment revenues	1,223	182	1,501	368
Operating Income
Total operating income	10,505	7,787	25,303	24,020
Total identifiable assets	572,073		572,073		565,563
Unregulated Energy [Member]
Total operating revenues, unaffiliated customers
Total operating revenues, unaffiliated customers	25,176	29,692	70,063	88,442
Intersegment Revenues
Total intersegment revenues
Operating Income
Total operating income	(401)	80	4,753	8,669
Total identifiable assets	70,166		70,166		107,916
Other [Member]
Total operating revenues, unaffiliated customers
Total operating revenues, unaffiliated customers	4,391	3,128	8,400	6,292
Intersegment Revenues
Total intersegment revenues	221	195	456	389
Operating Income
Total identifiable assets	37,461		37,461		35,587
Other and eliminations [Member]
Operating Income
Total operating income	$ 351	$ (91)	$ 472	$ (74)