Balancing and Memorandum Account Recovery Procedures (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
Jun. 28, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Memorandum Accounts [Roll Forward]
Beginning Balance		$ 7,971	$ (229)	$ 8,910	$ (1,377)
Revenue Increase(Reduction)		6,787	301	14,364	1,122
Refunds (Collections)		(2,751)	150	(4,506)	477
Surcharge Offset		(5,863)	0	(12,624)	0
Ending Balance		6,144	222	6,144	222
Balancing Accounts [Roll Forward]
Beginning Balance		38,013	42,950	36,296	48,437
Revenue Increase(Reduction)		2,594	1,834	11,639	3,380
Refunds (Collections)		(16,647)	(10,425)	(30,736)	(17,458)
Surcharge Offset		5,863	0	12,624	0
Ending Balance		29,823	34,359	29,823	34,359
Balancing and Memorandum Account [Roll Forward]
Beginning Balance		45,984	42,721	45,206	47,060
Revenue Increase (Reduction)		9,381	2,135	26,003	4,502
Refunds (Collections)		(19,398)	(10,275)	(35,242)	(16,981)
Surcharge Offset		0	0	0	0
Ending Balance		35,967	34,581	35,967	34,581
Net under-collected balancing and memorandum accounts		2,949		2,949
2014 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		1,563	0	2,944	0
Revenue Increase(Reduction)		164	0	11	0
Refunds (Collections)		(1,044)	0	(2,272)	0
Surcharge Offset		0	0	0	0
Ending Balance		683	0	683	0
Balancing and Memorandum Account [Roll Forward]
WCMA Reserve			1,267		1,267
2015 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		4,747	0	5,372	0
Revenue Increase(Reduction)		528	0	431	0
Refunds (Collections)		(1,883)	0	(2,411)	0
Surcharge Offset		0	0	0	0
Ending Balance		3,392	0	3,392	0
Balancing and Memorandum Account [Roll Forward]
WCMA Reserve			1,892		1,892
2016 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		0	0	0	0
Revenue Increase(Reduction)		5,863	0	12,624	0
Refunds (Collections)		0	0	0	0
Surcharge Offset		(5,863)	0	(12,624)	0
Ending Balance		0	0	0	0
Water supply costs
Balancing Accounts [Roll Forward]
Beginning Balance		2,641	1,070	2,771	890
Revenue Increase(Reduction)		2,420	2,153	2,364	2,445
Refunds (Collections)		452	(32)	378	(144)
Surcharge Offset		0	0	0	0
Ending Balance		5,513	3,191	5,513	3,191
Drought surcharges
Balancing Accounts [Roll Forward]
Beginning Balance		(1,716)	(80)	(359)	0
Revenue Increase(Reduction)		0	0	0	0
Refunds (Collections)		(10,467)	(6,333)	(18,585)	(6,413)
Surcharge Offset		5,863	0	12,624	0
Ending Balance		(6,320)	(6,413)	(6,320)	(6,413)
Pension
Balancing Accounts [Roll Forward]
Beginning Balance		(520)	140	(552)	1,412
Revenue Increase(Reduction)		280	(231)	840	(692)
Refunds (Collections)		(1,055)	(230)	(1,583)	(1,041)
Surcharge Offset		0	0	0	0
Ending Balance		(1,295)	(321)	(1,295)	(321)
2012 General Rate Case true-up
Balancing Accounts [Roll Forward]
Beginning Balance		27,740	40,367	33,070	44,400
Revenue Increase(Reduction)		0	0	0	1,937
Refunds (Collections)		(3,850)	(3,813)	(9,180)	(9,783)
Surcharge Offset		0	0	0	0
Ending Balance		23,890	36,554	23,890	36,554
2016 General Rate Case True-up [Member]
Balancing Accounts [Roll Forward]
Beginning Balance		8,767	0	0	0
Revenue Increase(Reduction)		0	0	8,767	0
Refunds (Collections)		(1,204)	0	(1,204)	0
Surcharge Offset		0	0	0	0
Ending Balance		7,563	0	7,563	0
Balancing and Memorandum Account [Roll Forward]
Balancing and Memorandum Account Previously Recorded	$ 185
All others
Memorandum Accounts [Roll Forward]
Beginning Balance		1,661	(229)	594	(1,377)
Revenue Increase(Reduction)		232	301	1,298	1,122
Refunds (Collections)		176	150	177	477
Surcharge Offset		0	0	0	0
Ending Balance		2,069	222	2,069	222
Balancing Accounts [Roll Forward]
Beginning Balance		1,101	1,453	1,366	1,735
Revenue Increase(Reduction)		(106)	(88)	(332)	(310)
Refunds (Collections)		(523)	(17)	(562)	(77)
Surcharge Offset		0	0	0	0
Ending Balance		$ 472	$ 1,348	$ 472	$ 1,348