Balancing and Memorandum Accounts (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		$ 25,549	$ 21,705
Regulatory Asset Increase (Decrease)		611	(2,031)
Refunds (Collections) Adjustments		(2,679)	2
Ending Balance		23,481	19,676
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		8,864	6,220
Regulatory Asset Increase (Decrease)		(558)	(321)
Refunds (Collections) Adjustments		(311)	0
Ending Balance		7,995	5,899
Balancing and Memorandum Account [Roll Forward]
Beginning Balance		34,413	27,925
Regulatory Asset Increase (Decrease)		53	(2,352)
Refunds (Collections)		(2,990)	2
Ending Balance		31,476	25,575
Total balance, net under-collection amount		$ 1,276
Authorized revenue, threshold percentage		2.00%
2014-2017 WCMA
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance	[1]	$ 7,750	6,679
Regulatory Asset Increase (Decrease)	[1]	0	375
Refunds (Collections) Adjustments	[1]	(838)	1
Ending Balance	[1]	6,912	7,055
2018 WCMA
Public Utilities, General Disclosures [Line Items]
Regulatory liability, due to sales in excess of authorized usage		(309)	(708)
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance	[1]	9,386	0
Regulatory Asset Increase (Decrease)	[1]	(389)	(708)
Refunds (Collections) Adjustments	[1]	0	0
Ending Balance	[1]	8,997	(708)
2019 WCMA
Public Utilities, General Disclosures [Line Items]
Regulatory liability, due to sales in excess of authorized usage		752
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		0	0
Regulatory Asset Increase (Decrease)		(752)	0
Refunds (Collections) Adjustments		0	0
Ending Balance		(752)	0
2012 General Rate Case true-up
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		11,328	11,319
Regulatory Asset Increase (Decrease)		95	0
Refunds (Collections) Adjustments		(1,271)	1
Ending Balance		10,152	11,320
Cost of capital memorandum account
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		(1,523)	(144)
Regulatory Asset Increase (Decrease)		(9)	(1,165)
Refunds (Collections) Adjustments		0	0
Ending Balance		(1,532)	(1,309)
Tax memorandum account
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		(6,504)	0
Regulatory Asset Increase (Decrease)		(41)	(933)
Refunds (Collections) Adjustments		0	0
Ending Balance		(6,545)	(933)
All others
Balancing and Memorandum Revenue Account [Roll Forward]
Beginning Balance		5,112	3,851
Regulatory Asset Increase (Decrease)		1,707	400
Refunds (Collections) Adjustments		(570)	0
Ending Balance		6,249	4,251
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		1,090	0
Regulatory Asset Increase (Decrease)		3	0
Refunds (Collections) Adjustments		(78)	0
Ending Balance		1,015	0
Water supply costs
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		9,617	8,679
Regulatory Asset Increase (Decrease)		(745)	(482)
Refunds (Collections) Adjustments		(655)	0
Ending Balance		8,217	8,197
Pension
Balancing and Memorandum Cost Recovery Account [Roll Forward]
Beginning Balance		(1,843)	(2,459)
Regulatory Asset Increase (Decrease)		184	161
Refunds (Collections) Adjustments		422	0
Ending Balance		(1,237)	(2,298)
2018 WCMA Reserve Recorded
Public Utilities, General Disclosures [Line Items]
Reserve recorded		$ (80)
2017 WCMA Reserve Recorded
Public Utilities, General Disclosures [Line Items]
Reserve recorded			$ (1,022)

[1] As of March 31, 2019, the reserve balances for the 2018 WCMA was $80 which has been included in the balances above. As of March 31, 2018, the reserve balance for the 2017 WCMA was $1,022 which has been included in the balance above.