Segment and Non-Tariffed Businesses Reporting (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) subsidiary reportable_segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of subsidiaries | subsidiary	4
Number of reportable segments | reportable_segment	2
Operating revenue	$ 573,686	$ 564,526	$ 420,482
Operating expense	462,527	446,856	363,003
Operating income (loss)	111,159	117,670	57,479
Net income (loss)	60,478	61,515	23,403
Depreciation and amortization	94,400	89,279	65,592
Senior note and other interest expense	54,339	54,255	31,796
Provision for income taxes	8,369	8,380	8,454
Assets	3,492,395	3,311,465	3,132,470
Regulated | Water Utility Services
Segment Reporting Information [Line Items]
Operating revenue	558,154	548,013	407,116
Operating expense	449,401	431,375	329,520
Operating income (loss)	108,753	116,638	77,596
Net income (loss)	67,530	69,245	42,691
Depreciation and amortization	91,896	86,758	63,775
Senior note and other interest expense	34,308	33,877	25,073
Provision for income taxes	10,327	16,563	8,382
Assets	3,380,637	3,197,626	3,016,846
Regulated | SJW Corp.
Segment Reporting Information [Line Items]
Operating revenue	558,154	548,013	407,116
Operating expense	449,401	431,375	329,520
Operating income (loss)	108,753	116,638	77,596
Net income (loss)	67,530	69,245	42,691
Depreciation and amortization	91,896	86,758	63,775
Senior note and other interest expense	34,308	33,877	25,073
Provision for income taxes	10,327	16,563	8,382
Assets	3,380,637	3,197,626	3,016,846
Non- tariffed | Water Utility Services
Segment Reporting Information [Line Items]
Operating revenue	10,153	10,981	7,969
Operating expense	7,138	6,943	5,443
Operating income (loss)	3,015	4,038	2,526
Net income (loss)	3,309	4,099	2,019
Depreciation and amortization	443	442	420
Senior note and other interest expense	0	0	0
Provision for income taxes	369	998	708
Assets	6,916	8,869	5,507
Non- tariffed | Real Estate Services
Segment Reporting Information [Line Items]
Operating revenue	5,379	5,532	5,397
Operating expense	3,585	3,510	3,751
Operating income (loss)	1,794	2,022	1,646
Net income (loss)	1,950	1,455	1,623
Depreciation and amortization	1,168	1,186	1,196
Senior note and other interest expense	0	0	0
Provision for income taxes	619	467	486
Assets	43,383	44,405	46,778
Non- tariffed | All Other
Segment Reporting Information [Line Items]
Operating revenue	0	0	0
Operating expense	2,403	5,028	24,289
Operating income (loss)	(2,403)	(5,028)	(24,289)
Net income (loss)	(12,311)	(13,284)	(22,930)
Depreciation and amortization	893	893	201
Senior note and other interest expense	20,031	20,378	6,723
Provision for income taxes	(2,946)	(9,648)	(1,122)
Assets	61,459	60,565	63,339
Non- tariffed | SJW Corp.
Segment Reporting Information [Line Items]
Operating revenue	15,532	16,513	13,366
Operating expense	13,126	15,481	33,483
Operating income (loss)	2,406	1,032	(20,117)
Net income (loss)	(7,052)	(7,730)	(19,288)
Depreciation and amortization	2,504	2,521	1,817
Senior note and other interest expense	20,031	20,378	6,723
Provision for income taxes	(1,958)	(8,183)	72
Assets	$ 111,758	$ 113,839	$ 115,624