Balancing and Memorandum Account Recovery Procedures (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 28, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Memorandum Accounts [Roll Forward]
Beginning Balance		$ 8,889	$ (789)	$ 8,910	$ (1,377)
Revenue Increase(Reduction)		4,069	397	7,580	821
Refunds (Collections)		(1,240)	163	(1,758)	327
Ending Balance		7,971	(229)	7,971	(229)
Memorandum Account, Surcharge Offset		(3,747)	0	(6,761)	0
Balancing Accounts [Roll Forward]
Beginning Balance		33,294	46,358	36,296	48,438
Revenue Increase(Reduction)		9,207	400	9,044	1,543
Refunds (Collections)		(8,235)	(3,809)	(14,088)	(7,032)
Surcharge Offset		3,747	0	6,761	0
Ending Balance		38,013	42,949	38,013	42,949
Balancing and Memorandum Account [Roll Forward]
Beginning Balance		42,183	45,569	45,206	47,061
Revenue Increase (Reduction)		13,276	797	16,624	2,364
Refunds (Collections)		(9,475)	(3,646)	(15,846)	(6,705)
Surcharge Offset		0	0	0	0
Ending Balance		45,984	42,720	45,984	42,720
Net under-collected balancing and memorandum accounts		3,074		3,074
Balancing and Memorandum Account Previously Recorded	$ 524
2014 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		2,427	0	2,944	0
Revenue Increase(Reduction)		(152)	0	(152)	0
Refunds (Collections)		(712)	0	(1,229)	0
Ending Balance		1,563	0	1,563	0
Memorandum Account, Surcharge Offset		0	0	0	0
Balancing and Memorandum Account [Roll Forward]
WCMA Reserve			1,431		1,431
2015 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		5,352	0	5,372	0
Revenue Increase(Reduction)		(77)	0	(97)	0
Refunds (Collections)		(528)	0	(528)	0
Ending Balance		4,747	0	4,747	0
Memorandum Account, Surcharge Offset		0	0	0	0
Balancing and Memorandum Account [Roll Forward]
WCMA Reserve			2,420		2,420
2016 WCMA
Memorandum Accounts [Roll Forward]
Beginning Balance		0	0	0	0
Revenue Increase(Reduction)		3,747	0	6,761	0
Refunds (Collections)		0	0	0	0
Ending Balance		0	0	0	0
Memorandum Account, Surcharge Offset		(3,747)	0	(6,761)	0
Water supply costs
Balancing Accounts [Roll Forward]
Beginning Balance		2,436	825	2,771	890
Revenue Increase(Reduction)		257	304	(56)	292
Refunds (Collections)		(52)	(59)	(74)	(112)
Surcharge Offset		0	0	0	0
Ending Balance		2,641	1,070	2,641	1,070
Drought surcharges
Balancing Accounts [Roll Forward]
Beginning Balance		(512)	0	(359)	0
Revenue Increase(Reduction)		0	0	0	0
Refunds (Collections)		(4,951)	(80)	(8,118)	(80)
Surcharge Offset		3,747	0	6,761	0
Ending Balance		(1,716)	(80)	(1,716)	(80)
Pension
Balancing Accounts [Roll Forward]
Beginning Balance		(427)	423	(552)	1,412
Revenue Increase(Reduction)		280	143	560	(463)
Refunds (Collections)		(373)	(427)	(528)	(810)
Surcharge Offset		0	0	0	0
Ending Balance		(520)	139	(520)	139
2012 General Rate Case true-up
Balancing Accounts [Roll Forward]
Beginning Balance		30,572	43,517	33,070	44,400
Revenue Increase(Reduction)		0	61	0	1,937
Refunds (Collections)		(2,832)	(3,211)	(5,330)	(5,970)
Surcharge Offset		0	0	0	0
Ending Balance		27,740	40,367	27,740	40,367
2016 General Rate Case True-up [Member]
Balancing Accounts [Roll Forward]
Beginning Balance		0	0	0	0
Revenue Increase(Reduction)		8,767	0	8,767	0
Refunds (Collections)		0	0	0	0
Surcharge Offset		0	0	0	0
Ending Balance		8,767	0	8,767	0
Balancing and Memorandum Account [Roll Forward]
Balancing and Memorandum Account Previously Recorded	$ 185
All others
Memorandum Accounts [Roll Forward]
Beginning Balance		1,110	(789)	594	(1,377)
Revenue Increase(Reduction)		551	397	1,068	821
Refunds (Collections)		0	163	(1)	327
Ending Balance		1,661	(229)	1,661	(229)
Memorandum Account, Surcharge Offset		0	0	0	0
Balancing Accounts [Roll Forward]
Beginning Balance		1,225	1,593	1,366	1,736
Revenue Increase(Reduction)		(97)	(108)	(227)	(223)
Refunds (Collections)		(27)	(32)	(38)	(60)
Surcharge Offset		0	0	0	0
Ending Balance		$ 1,101	$ 1,453	$ 1,101	$ 1,453