Financial Statement Schedule - Condensed Statements of Comprehensive Income (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 29, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Operating revenue		$ 573,686	$ 564,526	$ 420,482
Operating expense:
Administrative and general		87,332	79,741	66,301
Property taxes and other non-income taxes		30,964	29,886	19,068
Merger related expenses		0	0	15,768
Total operating expense		462,527	446,856	363,003
Operating income		111,159	117,670	57,479
Other (expense) income:
Interest on long-term debt, mortgage and other interest expense		(54,339)	(54,255)	(31,796)
Gain on sale of Texas Water Alliance (“TWA”)	$ 3,000	3,000	0	0
Interest income on money market fund		0	0	6,536
Other, net		6,770	5,906	2,091
Income before income taxes		68,847	69,895	32,081
Provision for income taxes		8,369	8,380	8,454
SJW Group net income		60,478	61,515	23,403
Other comprehensive income (loss), net		901	(1,190)	126
SJW Group comprehensive income		61,379	60,325	23,529
SJW Group
Condensed Financial Statements, Captions [Line Items]
Operating revenue		0	0	0
Operating expense:
Administrative and general		2,050	3,110	8,130
Property taxes and other non-income taxes		(38)	250	250
Merger related expenses		0	0	14,849
Total operating expense		2,012	3,360	23,229
Operating income		(2,012)	(3,360)	(23,229)
Other (expense) income:
Interest on long-term debt, mortgage and other interest expense		(18,673)	(19,430)	(6,615)
Gain on sale of Texas Water Alliance (“TWA”)		3,000	0	0
Interest income on money market fund		0	0	6,536
Other, net		(160)	(250)	89
Income before income taxes		(17,845)	(23,040)	(23,219)
Provision for income taxes		(4,660)	(6,414)	(1,431)
Equity earnings from subsidiaries, net of taxes		73,663	78,141	45,191
Subsidiaries
Other (expense) income:
Equity earnings from subsidiaries, net of taxes		$ 73,663	$ 78,141	$ 45,191