STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 1,652,730	$ 1,633,731	$ 1,539,633
Cost of natural gas	687,974	714,636	614,501
Operating expenses
Operations and maintenance	429,126	411,702	399,290
Depreciation and amortization	180,395	160,086	151,889
General taxes	59,977	58,878	57,225
Total operating expenses	669,498	630,666	608,404
Operating income	295,258	288,429	316,728
Other expense, net	(2,976)	(11,359)	(14,525)
Interest expense, net	(62,681)	(51,305)	(46,065)
Income before income taxes	229,601	225,765	256,138
Income taxes	(42,852)	(53,531)	(93,143)
Net income	$ 186,749	$ 172,234	$ 162,995
Earnings per share
Basic	$ 3.53	$ 3.27	$ 3.10
Diluted	$ 3.51	$ 3.25	$ 3.08
Average shares (thousands)
Basic	52,895	52,693	52,527
Diluted	53,240	53,029	52,979
Dividends declared per share of stock	$ 2.00	$ 1.84	$ 1.68