Summary of Significant Accounting Policies - Property, Plant and Equipment and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Major components of depreciable plant and equipment [Abstract]
Source of supply	$ 207,537	$ 191,082
Pumping plant	284,308	269,246
Water treatment plant	354,617	327,492
Transmission and distribution plant	2,820,358	2,615,640
General plant	301,091	257,825
Total depreciable plant and equipment	$ 3,967,911	$ 3,661,285
Useful Lives
Depreciation expense as percentage of beginning of year balance of depreciable plant	2.90%	3.30%	3.20%
Capitalized interest costs	$ 2,900	$ 4,703	$ 4,422
Equity funds capitalized	2,114	1,551	1,926
Water Plant
Useful Lives
Depreciation	$ 104,325	$ 99,413	$ 91,906
Minimum
Useful Lives
Source of supply	20 years
Pumping plant	5 years
Water treatment plant	5 years
Transmission and distribution plant	10 years
General plant	4 years
Useful life of intangible assets	5 years
Maximum
Useful Lives
Source of supply	100 years
Pumping plant	70 years
Water treatment plant	50 years
Transmission and distribution plant	100 years
General plant	61 years
Useful life of intangible assets	70 years