Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues:
Electric	$ 555,085	$ 592,491	$ 536,413
Gas	41,702	51,842	50,041
Other	8,786	7,997	7,876
Total operating revenues	605,573	652,330	594,330
Operating revenue deductions:
Fuel and purchased power	169,860	215,086	175,406
Cost of natural gas sold and transported	19,502	27,025	25,795
Regulated operating expenses	113,551	110,691	105,333
Other operating expenses	3,309	2,987	3,142
Maintenance and repairs	48,522	46,775	40,873
Loss on plant disallowance		86	2,409
Depreciation and amortization	80,550	73,185	69,306
Provision for income taxes	34,800	39,398	37,465
Other taxes	39,178	37,098	34,938
Total operating revenue deductions	509,272	552,331	494,667
Operating income	96,301	99,999	99,663
Other income and (deductions):
Allowance for equity funds used during construction	4,850	6,420	3,853
Interest income	145	51	566
Benefit for other income taxes	988	178	(27)
Other - non-operating expense, net	(3,429)	(1,302)	(1,218)
Total other income	2,554	5,347	3,174
Interest charges:
Long-term debt	43,802	40,637	40,354
Short-term debt	266	113	60
Allowance for borrowed funds used during construction	(2,845)	(3,497)	(2,087)
Other	1,035	990	1,065
Total interest charges	42,258	38,243	39,392
Net income	$ 56,597	$ 67,103	$ 63,445
Weighted average number of common shares outstanding - basic (in shares)	43,671	43,291	42,781
Weighted average number of common shares outstanding - diluted (in shares)	43,718	43,314	42,803
Total earnings per weighted average share of common stock - basic (in dollars per share)	$ 1.30	$ 1.55	$ 1.48
Total earnings per weighted average share of common stock - diluted (in dollars per share	1.29	1.55	1.48
Dividends declared per share of common stock (in dollars per share)	$ 1.04	$ 1.025	$ 1.005