Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
OPERATING REVENUE	$ 124,578	$ 112,344	$ 295,696	$ 260,400
Production Expenses:
Purchased water	30,833	28,681	66,938	52,863
Power	2,500	2,141	5,491	4,992
Groundwater extraction charges	15,756	10,867	34,098	25,627
Other production expenses	3,874	3,311	11,040	9,815
Total production expenses	52,963	45,000	117,567	93,297
Administrative and general	13,477	12,449	39,494	35,690
Maintenance	4,374	4,217	12,293	12,082
Property taxes and other non-income taxes	3,454	3,213	10,260	9,115
Depreciation and amortization	12,065	11,119	36,217	33,489
Total operating expense	86,333	75,998	215,831	183,673
OPERATING INCOME	38,245	36,346	79,865	76,727
OTHER (EXPENSE) INCOME:
Interest on long-term debt	(5,487)	(4,993)	(17,146)	(15,039)
Mortgage and other interest expense	(54)	(433)	(208)	(1,291)
Gain on sale of California Water Service Group stock	0	0	0	3,197
Gain on sale of real estate investments	0	124	6,903	124
Dividend income	18	17	54	70
Other, net	341	410	1,382	869
Income before income taxes	33,063	31,471	70,850	64,657
Provision for income taxes	13,523	12,512	27,055	25,545
NET INCOME BEFORE NONCONTROLLING INTEREST	19,540	18,959	43,795	39,112
Less net income attributable to the noncontrolling interest	0	0	1,896	0
SJW GROUP NET INCOME	19,540	18,959	41,899	39,112
Other comprehensive income, net of tax:
Unrealized gain on investment	80	(169)	252	848
Reclassification adjustment for gain realized on sale of investments	0	0	0	(1,742)
SJW GROUP COMPREHENSIVE INCOME	$ 19,620	$ 18,790	$ 42,151	$ 38,218
SJW GROUP EARNINGS PER SHARE
Basic (usd per share)	$ 0.95	$ 0.93	$ 2.04	$ 1.91
Diluted (usd per share)	0.94	0.92	2.03	1.90
DIVIDENDS PER SHARE (usd per share)	$ 0.22	$ 0.20	$ 0.65	$ 0.61
WEIGHTED AVERAGE SHARES OUTSTANDING
Basic (shares)	20,516,172	20,451,930	20,502,274	20,434,494
Diluted (shares)	20,697,097	20,602,410	20,675,479	20,580,728