Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Revenue	$ 1,949,102	$ 1,696,941	$ 1,734,900
Operating expenses:
Fuel, purchased power and cost of natural gas sold	741,934	492,404	570,829
Operations and maintenance	501,690	495,404	495,994
Depreciation, depletion and amortization	235,953	224,457	209,120
Taxes - property and production	60,096	56,373	52,915
Total operating expenses	1,539,673	1,268,638	1,328,858
Operating income	409,429	428,303	406,042
Other income (expense):
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(154,112)	(144,931)	(139,291)
Interest income	1,708	1,461	1,632
Impairment of investment	0	(6,859)	(19,741)
Other income (expense), net	1,404	(2,293)	(5,740)
Total other income (expense)	(151,000)	(152,622)	(163,140)
Income before income taxes	258,429	275,681	242,902
Income tax (expense)	(7,169)	(32,918)	(29,580)
Net income	251,260	242,763	213,322
Net income attributable to non-controlling interest	(14,516)	(15,155)	(14,012)
Net income available for common stock	$ 236,744	$ 227,608	$ 199,310
Earnings per share of common stock:
Earnings per share, Basic (usd per share)	$ 3.74	$ 3.65	$ 3.29
Earnings per share, Diluted (usd per share)	$ 3.74	$ 3.65	$ 3.28
Weighted average common shares outstanding:
Basic (in shares)	63,219	62,378	60,662
Diluted (in shares)	63,325	62,439	60,798