Summary of Significant Accounting Policies - Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory asset increase (decrease)	$ 8,779	$ 2,516
Revenue from contracts with customers	559,568	549,270	$ 447,720
Alternative revenue programs, net	5,304	(493)	(18,232)
Other balancing and memorandum accounts, net	5,138	11,856	(30,092)
Other regulatory mechanisms, net	(1,703)	(1,639)	15,689
Rental income	5,379	5,532	5,397
Operating revenue	573,686	564,526	420,482
Regulated operating revenue, water surcharge	5,691	4,911	4,955
WCMA
Regulatory Assets [Line Items]
Regulatory asset increase (decrease)	$ 3,243	$ 0
2018 WCMA | Advice Letter No. 532 | SJWC
Regulatory Assets [Line Items]
Regulatory asset increase (decrease)			(9,386)
2019 WCMA | Advice Letter No. 532 | SJWC
Regulatory Assets [Line Items]
Regulatory asset increase (decrease)			$ (639)