Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating revenues:
Electric	$ 510,653	$ 524,275	$ 484,715
Gas	39,849	46,430	50,885
Other	6,595	6,165	5,676
Total operating revenues	557,097	576,870	541,276
Operating revenue deductions:
Fuel and purchased power	178,896	200,256	199,299
Cost of natural gas sold and transported	18,633	22,760	26,614
Regulated operating expenses	94,371	85,442	79,292
Other operating expenses	2,730	2,098	1,950
Maintenance and repairs	40,444	41,041	36,771
Loss on plant disallowance		150
Depreciation and amortization	60,447	63,537	58,656
Provision for income taxes	34,096	34,071	30,470
Other taxes	31,259	30,581	27,729
Total operating revenue deductions	460,876	479,936	460,781
Operating income	96,221	96,934	80,495
Other income and (deductions):
Allowance for equity funds used during construction	1,147	294	4,538
Interest income	972	555	176
Provision for other income taxes	(63)	(227)	(63)
Other - non-operating expense, net	(1,910)	(1,283)	(1,039)
Total other income and (deductions)	146	(661)	3,612
Interest charges:
Long-term debt	40,192	42,581	41,959
Trust preferred securities			2,090
Short-term debt	187	86	631
Allowance for borrowed funds used during construction	(781)	(218)	(5,636)
Other	1,088	(1,147)	(2,333)
Total interest charges	40,686	41,302	36,711
Net income	$ 55,681	$ 54,971	$ 47,396
Weighted average number of common shares outstanding - basic (in shares)	42,257	41,852	40,545
Weighted average number of common shares outstanding - diluted (in shares)	42,284	41,887	40,580
Total earnings per weighted average share of common stock - basic and diluted (in dollars per share)	$ 1.32	$ 1.31	$ 1.17
Dividends declared per share of common stock (in dollars per share)	$ 1.00	$ 0.64	$ 1.28