Segment and Non-Tariffed Business Reporting - Schedule of Segment Reporting Information, by Segment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022 USD ($) reportingUnit	Mar. 31, 2021 USD ($)	Jun. 30, 2021 reportingUnit	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Operating revenue	$ 124,302	$ 114,785
Operating expense	107,713	101,706
Operating income (loss)	16,589	13,079
Net income (loss)	3,737	2,616
Depreciation and amortization	27,606	23,438
Interest on long-term debt and other interest expense	13,729	13,439
Provision (benefit) for income taxes	1,067	(896)
Assets	$ 3,511,876	3,332,142		$ 3,492,395
Number of reporting units | reportingUnit	2		2
Water Utility Services | Regulated
Segment Reporting Information [Line Items]
Operating revenue	$ 120,518	111,396
Operating expense	101,451	98,478
Operating income (loss)	19,067	12,918
Net income (loss)	9,715	5,699
Depreciation and amortization	24,511	22,817
Interest on long-term debt and other interest expense	8,763	8,171
Provision (benefit) for income taxes	2,020	(116)
Assets	3,403,006	3,218,536
Water Utility Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	2,428	2,045
Operating expense	3,979	1,369
Operating income (loss)	(1,551)	676
Net income (loss)	(1,317)	722
Depreciation and amortization	2,572	109
Interest on long-term debt and other interest expense	0	0
Provision (benefit) for income taxes	(437)	182
Assets	4,139	7,625
Real Estate Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	1,356	1,344
Operating expense	909	881
Operating income (loss)	447	463
Net income (loss)	308	323
Depreciation and amortization	300	289
Interest on long-term debt and other interest expense	0	0
Provision (benefit) for income taxes	103	109
Assets	44,361	44,763
All Other | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	0	0
Operating expense	1,374	978
Operating income (loss)	(1,374)	(978)
Net income (loss)	(4,969)	(4,128)
Depreciation and amortization	223	223
Interest on long-term debt and other interest expense	4,966	5,268
Provision (benefit) for income taxes	(619)	(1,071)
Assets	60,370	61,218
SJW Group | Regulated
Segment Reporting Information [Line Items]
Operating revenue	120,518	111,396
Operating expense	101,451	98,478
Operating income (loss)	19,067	12,918
Net income (loss)	9,715	5,699
Depreciation and amortization	24,511	22,817
Interest on long-term debt and other interest expense	8,763	8,171
Provision (benefit) for income taxes	2,020	(116)
Assets	3,403,006	3,218,536
SJW Group | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	3,784	3,389
Operating expense	6,262	3,228
Operating income (loss)	(2,478)	161
Net income (loss)	(5,978)	(3,083)
Depreciation and amortization	3,095	621
Interest on long-term debt and other interest expense	4,966	5,268
Provision (benefit) for income taxes	(953)	(780)
Assets	$ 108,870	$ 113,606