STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues	$ 1,808,597	$ 1,530,268	$ 1,652,730
Cost of natural gas	775,006	537,445	687,974
Operating expenses
Operations and maintenance	449,676	431,115	429,126
Depreciation and amortization	207,233	194,881	180,395
General taxes	66,424	63,311	59,977
Total operating expenses	723,333	689,307	669,498
Operating income	310,258	303,516	295,258
Other expense, net	(3,207)	(3,020)	(2,976)
Interest expense, net	(60,301)	(62,505)	(62,681)
Income before income taxes	246,750	237,991	229,601
Income taxes	(40,316)	(41,579)	(42,852)
Net income	$ 206,434	$ 196,412	$ 186,749
Earnings per share
Basic	$ 3.85	$ 3.70	$ 3.53
Diluted	$ 3.85	$ 3.68	$ 3.51
Average shares (thousands)
Basic	53,575	53,133	52,895
Diluted	53,674	53,370	53,240
Dividends declared per share of stock	$ 2.32	$ 2.16	$ 2.00