Regulated Operating Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Regulated Operating Expense
Electric transmission and distribution expense	$ 5,028	$ 4,108	$ 18,003	$ 15,647
Natural gas transmission and distribution expense	546	652	2,337	2,476
Power operation expense (other than fuel)	3,792	3,794	15,634	14,394
Customer accounts and assistance expense	2,579	2,434	10,356	10,108
Employee pension expense	2,643	2,536	10,287	9,496
Employee healthcare plan	2,786	2,238	10,374	8,056
General office supplies and expense	3,429	2,752	11,453	10,011
Administrative and general expense	4,315	4,219	15,187	14,868
Allowance for uncollectible accounts	746	593	3,191	3,935
Regulatory reversal of gain on sale of assets	1,236		1,236
Miscellaneous expense	37	22	102	84
Total	$ 27,137	$ 23,348	$ 98,160	$ 89,075