Segment and Non-Tariffed Business Reporting (Details) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)		Jun. 30, 2020 USD ($) subsidiary reportable_segment		Jun. 30, 2019 USD ($)		Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of subsidiaries | subsidiary						4
Number of reportable business segments | reportable_segment						2
Operating revenue		$ 147,209		$ 102,965		$ 262,963		$ 180,647
Operating expense		111,139		80,994		211,466		146,268
Operating income (loss)		36,070		21,971		51,497		34,379
Net income (loss)		19,721		13,538		22,138		19,411
Depreciation and amortization		22,753		15,101		44,135		30,246
Senior note and other interest expense		13,180		6,714		26,464		12,505
Income tax expense (benefit) in net income		4,210		4,192		4,648		6,237
Assets		3,209,977		2,003,650		3,209,977		2,003,650		$ 3,132,470	$ 2,003,650
Water Utility Services | Regulated
Segment Reporting Information [Line Items]
Operating revenue		143,072		99,773		254,439		174,920
Operating expense		107,185		75,564		203,202		136,149
Operating income (loss)		35,887		24,209		51,237		38,771
Net income (loss)		22,236		13,662		28,064		19,762
Depreciation and amortization		22,123		14,698		42,872		29,447
Senior note and other interest expense		8,289		6,170		16,463		11,390
Income tax expense (benefit) in net income		5,449		4,154		6,651		6,230
Assets		3,079,118		1,537,404		3,079,118		1,537,404		1,537,404
Water Utility Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		2,693		1,823		5,710		2,992
Operating expense		1,759		1,356		3,120		2,197
Operating income (loss)		934		467		2,590		795
Net income (loss)		881		336		2,351		572
Depreciation and amortization		108		105		216		202
Senior note and other interest expense		0		0		0		0
Income tax expense (benefit) in net income		260		130		730		222
Assets		9,913		6,149		9,913		6,149		6,149
Real Estate Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		1,444		1,369		2,814		2,735
Operating expense		850		1,008		1,681		1,899
Operating income (loss)		594		361		1,133		836
Net income (loss)		443		662		831		980
Depreciation and amortization		298		298		600		597
Senior note and other interest expense		0		0		0		0
Income tax expense (benefit) in net income		124		220		256		350
Assets		44,889		46,510		44,889		46,510		46,510
All Other | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		0	[1]	0	[1]	0		0
Operating expense		1,345	[1]	3,066	[1]	3,463		6,023
Operating income (loss)		(1,345)	[1]	(3,066)	[1]	(3,463)		(6,023)	[1]
Net income (loss)		(3,839)	[1]	(1,122)	[1]	(9,108)		(1,903)
Depreciation and amortization		224	[1]	0	[1]	447		0
Senior note and other interest expense		4,891	[1]	544	[1]	10,001		1,115
Income tax expense (benefit) in net income	[1]	(1,623)		(312)		(2,989)		(565)
Assets		76,057	[1]	413,587		76,057	[1]	413,587		$ 413,587
SJW Group | Regulated
Segment Reporting Information [Line Items]
Operating revenue		143,072		99,773		254,439		174,920
Operating expense		107,185		75,564		203,202		136,149
Operating income (loss)		35,887		24,209		51,237		38,771
Net income (loss)		22,236		13,662		28,064		19,762
Depreciation and amortization		22,123		14,698		42,872		29,447
Senior note and other interest expense		8,289		6,170		16,463		11,390
Income tax expense (benefit) in net income		5,449		4,154		6,651		6,230
Assets		3,079,118		1,537,404		3,079,118		1,537,404			1,537,404
SJW Group | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		4,137		3,192		8,524		5,727
Operating expense		3,954		5,430		8,264		10,119
Operating income (loss)		183		(2,238)		260		(4,392)
Net income (loss)		(2,515)		(124)		(5,926)		(351)
Depreciation and amortization		630		403		1,263		799
Senior note and other interest expense		4,891		544		10,001		1,115
Income tax expense (benefit) in net income		(1,239)		38		(2,003)		7
Assets		$ 130,859		$ 466,246		$ 130,859		$ 466,246			$ 466,246

[1] * The “All Other” category for the six months ended June 30, 2020, includes the accounts of SJW Group, SJWNE LLC and CTWS on a stand-alone basis. For the three months ended June 30, 2019, the “All Other” category includes the accounts of SJW Group and Hydro Sub, Inc. on a stand-alone basis. For the three months ended June 30, 2019, Hydro Sub, Inc. had no recorded revenue or expenses and as of June 30, 2019 held no assets and incurred no liabilities. Hydro Sub. Inc. was a subsidiary created solely to facilitate the merger with CTWS and was dissolved following the completion of merger in October 2019.