Regulated Operating Expense (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Regulated Operating Expense
Electric transmission and distribution expense	$ 6,836	$ 7,100	$ 28,629	$ 28,221
Natural gas transmission and distribution expense	706	677	2,727	2,365
Power operation expense (other than fuel)	4,053	5,317	16,999	17,415
Customer accounts and assistance expense	2,731	2,704	10,965	11,106
Employee pension expense	2,625	2,684	10,727	10,648
Employee healthcare expense	2,245	2,234	10,173	9,656
General office supplies and expense	4,339	2,834	15,944	13,666
Administrative and general expense	4,116	4,556	14,423	14,716
Allowance for uncollectible accounts	79	327	1,833	2,975
Miscellaneous expense	115	118	425	603
Total	$ 27,845	$ 28,551	$ 112,845	$ 111,371