Summary of Significant Accounting Policies Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 222,474	$ 214,963	$ 529,804	$ 499,840
Total operating revenue	304,108	232,537	605,155	537,679
Total non-regulated revenue	3,934	4,118	11,969	14,149
Regulated Water and WasteWater Services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	222,474	214,963	529,804	499,840
Regulatory balancing account revenue	81,634	17,574	75,351	37,839
Total operating revenue	304,108	232,537	605,155	537,679
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	151,938	139,137	360,935	330,745
Business
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	36,951	38,247	93,175	95,433
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,496	9,077	21,996	23,866
Public authorities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12,862	12,482	26,470	24,566
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,227	16,020	27,228	25,230
Operating and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,680	2,929	7,969	9,248
Other non-regulated revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	625	626	2,223	3,189
Non-Regulated Services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,305	3,555	10,192	12,437
Lease Income	629	563	1,777	1,712
Total non-regulated revenue	$ 3,934	$ 4,118	$ 11,969	$ 14,149