Segment and Non-Tariffed Business Reporting - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Operating revenue	$ 176,174		$ 156,886		$ 325,556	$ 294,182
Operating expense	135,604		125,728		257,073	237,846
Operating income (loss)	40,570		31,158		68,483	56,336
Net income (loss)	20,696	$ 11,699	18,286	$ 11,530	32,395	29,816
Depreciation and amortization	28,366		26,121		56,736	52,417
Interest on long-term debt and other interest expense	18,294		16,397		35,878	32,169
Provision (benefit) for income taxes	3,724		(1,512)		5,955	(434)
Total assets	4,439,427				4,439,427		$ 4,345,067
Water Utility Services
Segment Reporting Information [Line Items]
Total assets	4,364,219				4,364,219		4,242,704
Water Utility Services | Regulated
Segment Reporting Information [Line Items]
Operating revenue	172,046		152,525		316,961	285,797
Operating expense	132,249		122,678		250,030	231,545
Operating income (loss)	39,797		29,847		66,931	54,252
Net income (loss)	23,956		20,510		38,556	33,732
Depreciation and amortization	28,057		25,811		56,118	51,497
Interest on long-term debt and other interest expense	12,037		10,846		23,579	21,393
Provision (benefit) for income taxes	5,325		102		9,021	2,826
Total assets	4,321,187				4,321,187		4,199,172
Water Utility Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	3,351		2,945		6,043	5,522
Operating expense	2,379		1,789		3,989	3,203
Operating income (loss)	972		1,156		2,054	2,319
Net income (loss)	498		596		1,230	1,214
Depreciation and amortization	85		85		170	169
Interest on long-term debt and other interest expense	224		0		445	0
Provision (benefit) for income taxes	301		320		619	643
Total assets	43,032				43,032		43,532
Real Estate Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	777		1,416		2,552	2,863
Operating expense	460		661		1,186	1,560
Operating income (loss)	317		755		1,366	1,303
Net income (loss)	(200)		544		583	969
Depreciation and amortization	1		1		2	304
Interest on long-term debt and other interest expense	0		0		0	0
Provision (benefit) for income taxes	(68)		243		198	385
Total assets	20,742				20,742		44,222
All Other | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	0		0		0	0
Operating expense	516		600		1,868	1,538
Operating income (loss)	(516)		(600)		(1,868)	(1,538)
Net income (loss)	(3,558)		(3,364)		(7,974)	(6,099)
Depreciation and amortization	223		224		446	447
Interest on long-term debt and other interest expense	6,033		5,551		11,854	10,776
Provision (benefit) for income taxes	(1,834)		(2,177)		(3,883)	(4,288)
Total assets	54,466				54,466		58,141
SJW Group | Regulated
Segment Reporting Information [Line Items]
Operating revenue	172,046		152,525		316,961	285,797
Operating expense	132,249		122,678		250,030	231,545
Operating income (loss)	39,797		29,847		66,931	54,252
Net income (loss)	23,956		20,510		38,556	33,732
Depreciation and amortization	28,057		25,811		56,118	51,497
Interest on long-term debt and other interest expense	12,037		10,846		23,579	21,393
Provision (benefit) for income taxes	5,325		102		9,021	2,826
Total assets	4,321,187				4,321,187		4,199,172
SJW Group | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	4,128		4,361		8,595	8,385
Operating expense	3,355		3,050		7,043	6,301
Operating income (loss)	773		1,311		1,552	2,084
Net income (loss)	(3,260)		(2,224)		(6,161)	(3,916)
Depreciation and amortization	309		310		618	920
Interest on long-term debt and other interest expense	6,257		5,551		12,299	10,776
Provision (benefit) for income taxes	(1,601)		$ (1,614)		(3,066)	$ (3,260)
Total assets	$ 118,240				$ 118,240		$ 145,895