Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Operating revenue	$ 790,909	$ 794,307	$ 714,557
Operations:
Purchased water	225,020	230,076	212,461
Purchased power	37,112	34,006	31,362
Pump taxes	15,342	12,647	11,518
Administrative and general	126,686	117,058	108,617
Other operations	86,392	95,859	90,061
Maintenance	29,592	28,026	26,834
Depreciation and amortization	108,715	98,505	89,220
Income taxes	2,805	11,435	16,280
Property and other taxes	32,475	30,029	28,792
Total operating expenses	664,139	657,641	615,145
Net operating income	126,770	136,666	99,412
Other income and expenses:
Non-regulated revenue	22,761	16,922	19,205
Non-regulated expenses	(17,234)	(14,300)	(13,869)
Other components of net periodic benefit credit (cost)	9,903	(4,988)	(5,733)
Allowance for equity funds used during construction	3,186	4,976	6,685
Gain on sale of non-utility property	94	0	28
Income tax expense on other income and expenses	(1,287)	(583)	(1,391)
Net other income	17,423	2,027	4,925
Interest expense:
Interest expense	44,980	45,047	44,891
Allowance for borrowed funds used during construction	(1,766)	(3,185)	(3,670)
Net interest expense	43,214	41,862	41,221
Net income	100,979	96,831	63,116
Net loss attributable to noncontrolling interests	(146)	0	0
Net income	$ 101,125	$ 96,831	$ 63,116
Earnings per share:
Basic (in dollars per share)	$ 1.96	$ 1.97	$ 1.31
Diluted (in dollars per share)	$ 1.96	$ 1.97	$ 1.31
Weighted average number of common shares outstanding:
Basic (in shares)	51,633	49,274	48,168
Diluted (in shares)	51,633	49,274	48,168