CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating revenues:
Electric	$ 127,026	$ 124,091	$ 255,788	$ 243,817	$ 522,624	$ 519,403
Gas	7,777	5,804	28,270	21,487	46,632	39,625
Other	1,843	1,737	3,728	3,472	6,851	6,797
Total operating revenues	136,646	131,632	287,786	268,776	576,107	565,825
Operating revenue deductions:
Fuel and purchased power	42,013	45,528	87,316	90,757	175,456	189,568
Cost of natural gas sold and transported	3,113	1,769	15,038	10,350	23,321	18,359
Regulated operating expenses	26,647	22,844	53,784	46,192	101,963	92,834
Other operating expenses	872	771	1,665	1,369	3,026	2,493
Maintenance and repairs	9,933	10,797	19,090	19,920	39,613	41,180
Loss on plant disallowance			2,409		2,409
Depreciation and amortization	17,635	15,068	33,736	30,003	64,180	59,318
Provision for income taxes	7,042	6,673	14,496	12,757	35,835	33,971
Other taxes	8,281	7,420	17,284	15,855	32,689	30,577
Total operating revenue deductions	115,536	110,870	244,818	227,203	478,492	468,300
Operating income	21,110	20,762	42,968	41,573	97,615	97,525
Other income and (deductions):
Allowance for equity funds used during construction	867	53	1,393	103	2,437	326
Interest income	10	123	517	302	1,187	819
Benefit/(provision) for other income taxes	(7)	(87)	(35)	(202)	105	(462)
Other - non-operating expense, net	(290)	(202)	(579)	(429)	(2,060)	(1,252)
Total other income and (deductions)	580	(113)	1,296	(226)	1,669	(569)
Interest charges:
Long-term debt	10,190	9,637	20,141	20,292	40,042	41,599
Short-term debt	12	129	59	159	87	199
Allowance for borrowed funds used during construction	(472)	(118)	(777)	(167)	(1,392)	(304)
Other	302	293	554	551	1,091	1,075
Total interest charges	10,032	9,941	19,977	20,835	39,828	42,569
Net income	$ 11,658	$ 10,708	$ 24,287	$ 20,512	$ 59,456	$ 54,387
Weighted average number of common shares outstanding - basic (in shares)	42,707	42,197	42,636	42,122	42,512	42,042
Weighted average number of common shares outstanding - diluted (in shares)	42,727	42,220	42,652	42,143	42,526	42,061
Total earnings per weighted average share of common stock - basic and diluted (in dollars per share)	$ 0.27	$ 0.25	$ 0.57	$ 0.49	$ 1.40	$ 1.29
Dividends declared per share of common stock (in dollars per share)	$ 0.25	$ 0.25	$ 0.50	$ 0.50	$ 1.00	$ 0.50