CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Operating revenues:
Electric	$ 128,762	$ 119,726	$ 519,690	$ 515,641
Gas	20,493	15,683	44,659	41,124
Other	1,885	1,735	6,745	6,521
Total operating revenues	151,140	137,144	571,094	563,286
Operating revenue deductions:
Fuel and purchased power	45,303	45,229	178,971	191,268
Cost of natural gas sold and transported	11,925	8,581	21,977	19,302
Regulated operating expenses	27,137	23,348	98,160	89,075
Other operating expenses	794	598	2,926	2,221
Maintenance and repairs	9,157	9,124	40,476	40,923
Loss on plant disallowance	2,409		2,409	150
Depreciation and amortization	16,100	14,935	61,612	61,138
Provision for income taxes	7,454	6,084	35,466	32,886
Other taxes	9,003	8,435	31,828	30,426
Total operating revenue deductions	129,282	116,334	473,825	467,389
Operating income	21,858	20,810	97,269	95,897
Other income and (deductions):
Allowance for equity funds used during construction	526	50	1,623	343
Interest income	508	179	1,300	712
Benefit (provision) for other income taxes	(28)	(115)	25	(366)
Other - non-operating expense, net	(289)	(227)	(1,973)	(1,224)
Total other income and (deductions)	717	(113)	975	(535)
Interest charges:
Long-term debt	9,951	10,654	39,488	42,603
Short-term debt	47	30	205	85
Allowance for borrowed funds used during construction	(305)	(48)	(1,038)	(243)
Other	252	257	1,083	63
Total interest charges	9,945	10,893	39,738	42,508
Net income	$ 12,630	$ 9,804	$ 58,506	$ 52,854
Weighted average number of common shares outstanding - basic (in shares)	42,564	42,047	42,385	41,946
Weighted average number of common shares outstanding - diluted (in shares)	42,587	42,075	42,401	41,968
Total earnings per weighted average share of common stock - basic and diluted (in dollars per share)	$ 0.30	$ 0.23	$ 1.38	$ 1.26
Dividends declared per share of common stock (in dollars per share)	$ 0.25	$ 0.25	$ 1.00	$ 0.57