Property, Plant And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Utility plant and equipment	$ 7,980,034	$ 7,404,399
Net utility plant acquisition adjustment	15,248
Total property, plant and equipment	8,201,936	7,648,469
Mains And Accessories [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	3,585,506	3,344,910
Services, Hydrants, Treatment Plants And Reservoirs [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	2,152,397	1,984,164
Operations Structures And Water Tanks [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	332,812	313,531
Miscellaneous Pumping And Purification Equipment [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	904,757	847,279
Meters, Data Processing, Transportation And Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	847,945	806,978
Land And Other Non-Depreciable Assets [Member]
Property, Plant and Equipment [Line Items]
Utility plant and equipment	156,617	107,537
Utility Construction Work In progress [Member]
Property, Plant and Equipment [Line Items]
Utility construction work in progress	214,633	235,979
Net Utility Plant Acquisition Adjustment [Member]
Property, Plant and Equipment [Line Items]
Net utility plant acquisition adjustment	(15,248)	(20,832)
Non-Utility Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Non-utility plant and equipment	$ 22,517	$ 28,923
Minimum [Member] | Mains And Accessories [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	33 years
Minimum [Member] | Services, Hydrants, Treatment Plants And Reservoirs [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Minimum [Member] | Operations Structures And Water Tanks [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	14 years
Minimum [Member] | Miscellaneous Pumping And Purification Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	9 years
Minimum [Member] | Meters, Data Processing, Transportation And Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Minimum [Member] | Net Utility Plant Acquisition Adjustment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	2 years
Minimum [Member] | Non-Utility Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	2 years
Maximum [Member] | Mains And Accessories [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	94 years
Maximum [Member] | Services, Hydrants, Treatment Plants And Reservoirs [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	89 years
Maximum [Member] | Operations Structures And Water Tanks [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	85 years
Maximum [Member] | Miscellaneous Pumping And Purification Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	76 years
Maximum [Member] | Meters, Data Processing, Transportation And Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	84 years
Maximum [Member] | Net Utility Plant Acquisition Adjustment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	59 years
Maximum [Member] | Non-Utility Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	64 years
Weighted Average [Member] | Mains And Accessories [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	75 years
Weighted Average [Member] | Services, Hydrants, Treatment Plants And Reservoirs [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	56 years
Weighted Average [Member] | Operations Structures And Water Tanks [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	48 years
Weighted Average [Member] | Miscellaneous Pumping And Purification Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	42 years
Weighted Average [Member] | Meters, Data Processing, Transportation And Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	29 years
Weighted Average [Member] | Net Utility Plant Acquisition Adjustment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	28 years
Weighted Average [Member] | Non-Utility Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	57 years