Balancing and Memorandum Account Recovery Procedures (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 04, 2018
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		$ 19,276	$ 29,016	$ 21,706	$ 25,909
Regulatory Asset Increase (Decrease)		3,691	6,550	1,251	21,136
Refunds (Collections) Adjustments		4	(9,085)	14	(20,634)
Surcharge Offset		0	6	0	76
Ending Balance		22,971	26,487	22,971	26,487
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		7,250	0	6,220	0
Regulatory Asset Increase (Decrease)		2,527	0	3,556	0
Refunds (Collections) Adjustments		0	0	1	0
Surcharge Offset		0	0	0	0
Ending Balance		9,777	0	9,777	0
Balancing and Memorandum Account [Roll Forward]
Beginning Balance		26,526	29,016	27,926	25,909
Regulatory Asset Increase (Decrease)		6,218	6,550	4,807	21,136
Refunds (Collections)		4	(9,085)	15	(20,634)
Surcharge Offset		0	6	0	76
Ending Balance		32,748	26,487	32,748	26,487
Memorandum Account, Authorized Recovery						$ 20,725
Regulatory Balancing and Memorandum Accounts, Net Under-Collected		$ 3,904		$ 3,904
Regulatory Balancing and Memorandum Accounts Review, Authorized Revenue, Threshold Percentage		2.00%		2.00%
2014-2016 WCMA
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		$ 365	3,003	$ 190	1,589
Regulatory Asset Increase (Decrease)		100	44	272	4,697
Refunds (Collections) Adjustments		1	(2,665)	4	(4,452)
Surcharge Offset		0	0	0	(1,452)
Ending Balance		466	382	466	382
2017 WCMA
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance	[1]	6,912	1,001	6,489	0
Regulatory Asset Increase (Decrease)	[1]	28	3,954	451	11,003
Refunds (Collections) Adjustments	[1]	0	0	0	0
Surcharge Offset	[1]	0	6	0	(6,042)
Ending Balance	[1]	6,940	4,961	6,940	4,961
2018 WCMA
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance	[1]	3,003	0	0	0
Regulatory Asset Increase (Decrease)	[1]	4,064	0	7,067	0
Refunds (Collections) Adjustments	[1]	0	0	0	0
Surcharge Offset	[1]	0	0	0	0
Ending Balance	[1]	7,067	0	7,067	0
Balancing and Memorandum Account [Roll Forward]
Memorandum Account, Revenue Increase (Reduction)		(4,660)		(8,070)
2012 General Rate Case true-up
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		11,324	15,765	11,320	20,682
Regulatory Asset Increase (Decrease)		0	0	0	0
Refunds (Collections) Adjustments		2	(4,123)	6	(9,040)
Surcharge Offset		0	0	0	0
Ending Balance		11,326	11,642	11,326	11,642
2015 General Rate Case true-up
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		117	2,411	115	5,528
Regulatory Asset Increase (Decrease)		0	0	0	0
Refunds (Collections) Adjustments		1	(2,297)	3	(5,414)
Surcharge Offset			0	0	0
Ending Balance		118	114	118	114
Cost of capital
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		(1,507)	(144)	(144)	(817)
Regulatory Asset Increase (Decrease)		(8)	0	(1,371)	0
Refunds (Collections) Adjustments		0	0	0	673
Surcharge Offset		0	0	0	0
Ending Balance		(1,515)	(144)	(1,515)	(144)
Tax memorandum
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		(5,496)	0	0	0
Regulatory Asset Increase (Decrease)		(459)	0	(5,955)	0
Refunds (Collections) Adjustments		0	0	0	0
Surcharge Offset		0	0	0	0
Ending Balance		(5,955)	0	(5,955)	0
Drought surcharges
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		0	(961)	0	(7,688)
Regulatory Asset Increase (Decrease)		0	0	0	0
Refunds (Collections) Adjustments		0	0	0	(767)
Surcharge Offset		0	0	0	7,494
Ending Balance		0	(961)	0	(961)
Cost-Recovery Accounts [Member]
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		0	4,407	0	3,181
Regulatory Asset Increase (Decrease)		0	2,502	0	4,503
Refunds (Collections) Adjustments		0	0	0	(775)
Surcharge Offset		0	0	0	0
Ending Balance		0	6,909	0	6,909
Water supply costs
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		9,387	0	8,679	0
Regulatory Asset Increase (Decrease)		2,366	0	3,074	0
Refunds (Collections) Adjustments		0	0	0	0
Surcharge Offset		0	0	0	0
Ending Balance		11,753	0	11,753	0
Pension
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		(2,137)	0	(2,459)	0
Regulatory Asset Increase (Decrease)		161	0	482	0
Refunds (Collections) Adjustments		0	0	1	0
Surcharge Offset		0	0	0	0
Ending Balance		(1,976)	0	(1,976)	0
All others
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		4,558	3,534	3,736	3,434
Regulatory Asset Increase (Decrease)		(34)	50	787	933
Refunds (Collections) Adjustments		0	0	1	(859)
Surcharge Offset		0	0	0	76
Ending Balance		4,524	$ 3,584	4,524	3,584
2017 WCMA Reserve Recorded
Balancing and Memorandum Account [Roll Forward]
Memorandum Account, Revenue Increase (Reduction)				(985)	$ (1,142)
2018 WCMA Reserve Recorded
Balancing and Memorandum Account [Roll Forward]
Memorandum Account, Revenue Increase (Reduction)		$ (596)		$ (1,003)

[1] As of September 30, 2018, the reserve balances for the 2017 and 2018 WCMA were $985 and $1,003, respectively, which have been netted from the balances above. As of September 30, 2017, the reserve balance for the 2017 WCMA was $1,142 which has been netted from the balance above.