Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Operating revenues:
Electric	$ 142,641	$ 153,089	$ 582,043	$ 560,740
Gas	19,818	24,609	47,051	54,157
Other	2,085	1,975	8,107	7,966
Total operating revenues	164,544	179,673	637,201	622,863
Operating revenue deductions:
Fuel and purchased power	48,977	55,586	208,477	185,690
Cost of natural gas sold and transported	11,423	15,045	23,403	28,914
Regulated operating expenses	28,551	27,957	111,285	106,153
Other operating expenses	805	716	3,076	3,064
Maintenance and repairs	10,267	10,257	46,784	41,973
Loss on plant disallowance			86
Depreciation and amortization	20,020	17,940	75,264	71,146
Provision for income taxes	8,884	12,174	36,108	42,185
Other taxes	10,904	10,510	37,493	36,445
Total operating revenue deductions	139,831	150,185	541,976	515,570
Operating income	24,713	29,488	95,225	107,293
Other income and (deductions):
Allowance for equity funds used during construction	978	1,252	6,147	4,579
Interest income	11	41	20	100
Benefit for other income taxes	113	53	237	54
Other - non-operating expense, net	(698)	(345)	(1,655)	(1,273)
Total other income	404	1,001	4,749	3,460
Interest charges:
Long-term debt	10,751	10,105	41,283	40,509
Short-term debt	73	5	181	17
Allowance for borrowed funds used during construction	(564)	(741)	(3,320)	(2,522)
Other	220	215	995	1,028
Total interest charges	10,480	9,584	39,139	39,032
Net income	$ 14,637	$ 20,905	$ 60,835	$ 71,721
Weighted average number of common shares outstanding - basic (in shares)	43,531	43,111	43,395	42,916
Weighted average number of common shares outstanding - diluted (in shares)	43,612	43,144	43,460	42,936
Total earnings per weighted average share of common stock - basic and diluted (in dollars per share)	$ 0.34	$ 0.48	$ 1.40	$ 1.67
Dividends declared per share of common stock (in dollars per share)	$ 0.26	$ 0.255	$ 1.03	$ 1.01