Consolidated Statements of Comprehensive Income - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Operating revenue	$ 670,363,000	$ 620,698,000	$ 573,686,000
Production Expenses:
Purchased water	135,982,000	122,334,000	98,231,000
Power	9,602,000	8,889,000	13,511,000
Groundwater extraction charges	62,980,000	56,158,000	75,866,000
Other production expenses	47,636,000	45,409,000	41,475,000
Total production expenses	256,200,000	232,790,000	229,083,000
Administrative and general	98,656,000	95,404,000	87,332,000
Maintenance	25,729,000	30,734,000	26,031,000
Property taxes and other non-income taxes	34,475,000	32,572,000	30,964,000
Depreciation and amortization	105,868,000	104,417,000	94,400,000
Gain on sale of nonutility properties	0	(6,197,000)	(7,494,000)
Impairment of long-lived asset	0	0	2,211,000
Total operating expense	520,928,000	489,720,000	462,527,000
Operating income	149,435,000	130,978,000	111,159,000
Other (expense) income:
Interest on long-term debt and other interest expense	(66,144,000)	(58,062,000)	(54,339,000)
Pension non-service (cost) credit	(1,230,000)	5,023,000	1,330,000
Other, net	8,882,000	4,385,000	10,697,000
Income before income taxes	90,943,000	82,324,000	68,847,000
Provision for income taxes	5,956,000	8,496,000	8,369,000
Net income	84,987,000	73,828,000	60,478,000
Other comprehensive income:
Unrealized gain (loss) on investment, net of taxes of $166 in 2023, $(188) in 2022 and $68 in 2021	530,000	(511,000)	185,000
Adjustment to pension benefit plans, net of taxes of $80 in 2023, $793 in 2022 and $264 in 2021	(216,000)	2,151,000	716,000
Comprehensive income	$ 85,301,000	$ 75,468,000	$ 61,379,000
Earnings per share
—Basic (in dollars per share)	$ 2.69	$ 2.44	$ 2.04
—Diluted (in dollars per share)	$ 2.68	$ 2.43	$ 2.03
Weighted average shares outstanding
—Basic (shares)	31,575,197	30,304,557	29,601,284
—Diluted (shares)	31,663,274	30,423,735	29,735,533