CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenues:
Electric	$ 150,370	$ 152,730	$ 406,158	$ 396,546	$ 520,265	$ 514,515
Gas	4,952	4,999	33,222	26,486	46,585	39,571
Other	2,164	1,473	5,892	4,945	7,542	6,657
Total operating revenues	157,486	159,202	445,272	427,977	574,392	560,743
Operating revenue deductions:
Fuel and purchased power	44,864	48,036	132,179	138,792	172,283	183,288
Cost of natural gas sold and transported	1,191	1,251	16,229	11,601	23,262	18,384
Regulated operating expenses	26,100	24,038	79,884	70,230	104,024	93,572
Other operating expenses	805	776	2,470	2,145	3,056	2,763
Maintenance and repairs	10,674	10,972	29,764	30,893	39,315	42,261
Loss on plant disallowance			2,409		2,409
Depreciation and amortization	17,735	15,108	51,471	45,111	66,807	59,669
Provision for income taxes	14,197	15,428	28,693	28,185	34,603	33,727
Other taxes	9,024	8,311	26,309	24,166	33,402	30,722
Total operating revenue deductions	124,590	123,920	369,408	351,123	479,161	464,386
Operating income	32,896	35,282	75,864	76,854	95,231	96,357
Other income and (deductions):
Allowance for equity funds used during construction	1,128	292	2,521	395	3,273	537
Interest income	5	265	522	568	926	1,055
Benefit/(provision) for other income taxes	47	(49)	12	(251)	201	(531)
Other - non-operating expense, net	(333)	(274)	(912)	(703)	(2,119)	(1,005)
Total other income and (deductions)	847	234	2,143	9	2,281	56
Interest charges:
Long-term debt	10,102	9,950	30,243	30,242	40,194	40,896
Short-term debt		16	59	175	71	192
Allowance for borrowed funds used during construction	(606)	(243)	(1,383)	(410)	(1,754)	(470)
Other	251	251	805	802	1,091	1,050
Total interest charges	9,747	9,974	29,724	30,809	39,602	41,668
Net income	$ 23,996	$ 25,542	$ 48,283	$ 46,054	$ 57,910	$ 54,745
Weighted average number of common shares outstanding - basic (in shares)	42,869	42,345	42,715	42,197	42,644	42,141
Weighted average number of common shares outstanding - diluted (in shares)	42,898	42,374	42,737	42,220	42,665	42,163
Total earnings per weighted average share of common stock - basic and diluted (in dollars per share)	$ 0.56	$ 0.60	$ 1.13	$ 1.09	$ 1.36	$ 1.30
Dividends declared per share of common stock (in dollars per share)	$ 0.25	$ 0.25	$ 0.75	$ 0.75	$ 1.00	$ 0.75