Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
REVENUE	$ 75,042	$ 69,045
Production Expenses:
Purchased water	15,416	13,924
Power	1,268	1,287
Groundwater extraction charges	9,532	7,410
Other production expenses	4,212	3,859
Total production expenses	30,428	26,480
Administrative and general	11,568	11,149
Maintenance	4,460	3,898
Property taxes and other non-income taxes	3,866	3,695
Depreciation and amortization	13,583	12,119
Merger related expenses	3,806	0
Total operating expense	67,711	57,341
OPERATING INCOME	7,331	11,704
OTHER (EXPENSE) INCOME:
Interest on long-term debt and other interest expense	(6,052)	(6,057)
Pension non-service cost	(583)	(871)
Unrealized loss on California Water Service Group stock	(667)	0
Other, net	676	463
Income before income taxes	705	5,239
Provision for income taxes	(580)	1,568
SJW GROUP NET INCOME	1,285	3,671
Other comprehensive income, net of tax:
Unrealized gain on investment	0	116
SJW GROUP COMPREHENSIVE INCOME	$ 1,285	$ 3,787
SJW GROUP EARNINGS PER SHARE
Basic (usd per share)	$ 0.06	$ 0.18
Diluted (usd per share)	0.06	0.18
DIVIDENDS PER SHARE (usd per share)	$ 0.28	$ 0.22
WEIGHTED AVERAGE SHARES OUTSTANDING
Basic (shares)	20,561,329	20,485,968
Diluted (shares)	20,701,031	20,655,239