Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Operating revenue	$ 420,482	$ 397,699	$ 389,225
Production Expenses:
Purchased water	99,118	97,378	86,456
Power	7,443	6,180	7,295
Groundwater extraction charges	43,917	46,770	47,817
Other production expenses	25,291	18,398	16,571
Total production expenses	175,769	168,726	158,139
Administrative and general	66,301	48,933	48,940
Maintenance	20,505	18,414	18,361
Property taxes and other non-income taxes	19,068	14,975	13,642
Depreciation and amortization	65,592	54,601	48,292
Merger related expenses	15,768	18,610	0
Total operating expense	363,003	324,259	287,374
Operating income	57,479	73,440	101,851
Other (expense) income:
Interest on long-term debt, mortgage and other interest expense	(31,796)	(24,332)	(22,929)
Pension non-service cost	(3,158)	(2,356)	(3,772)
Unrealized loss on California Water Service Group stock	0	(527)	0
Gain on sale of California Water Service Group stock	0	104	0
(Loss) gain on sale of utility property	(20)	9	12,499
Gain on sale of real estate investments	929	0	6,903
Other, net	6,536	155	0
Other, net	2,111	2,339	1,941
Income before income taxes	32,081	48,832	96,493
Provision for income taxes	8,454	10,065	35,393
Net income before noncontrolling interest	23,627	38,767	61,100
Less net income attributable to the noncontrolling interest	224	0	1,896
SJW Group net income	23,403	38,767	59,204
Other comprehensive income:
Unrealized gain on investment, net of taxes of $43 in 2019, $0 in 2018 and $466 in 2017	117	0	679
Adjustment to pension benefit plans, net of taxes of $22 in 2019	(9)	0	0
SJW Group comprehensive income	$ 23,529	$ 38,767	$ 59,883
SJW Group earnings per share
—Basic (in dollars per share)	$ 0.82	$ 1.83	$ 2.89
—Diluted (in dollars per share)	$ 0.82	$ 1.82	$ 2.86
Weighted average shares outstanding
—Basic (shares)	28,443,052	21,214,277	20,506,960
—Diluted (shares)	28,562,546	21,332,387	20,685,118