Summary of Significant Accounting Policies (Balancing and Memorandum Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Balancing and Memorandum Accounts [Line Items]
Memorandum Account, Beginning Balance	$ (1,377)	$ (1,896)	$ (1,887)
Memorandum Account, Revenue Increase (Reduction)	21,986	341	869
Memorandum Account, Refunds (Collections)	440	178	(878)
Memorandum Account, Surcharge Offset	(12,139)	0	0
Memorandum Account, Ending Balance	8,910	(1,377)	(1,896)
Balancing Account, Beginning Balance	48,438	9,585	5,436
Balancing Account, Revenue Increase (Reduction)	2,745	41,657	4,149
Balancing Account, Refunds (Collections)	(27,026)	(2,804)	0
Balancing Account, Surcharge Offset	12,139	0	0
Balancing Account, Ending Balance	36,296	48,438	9,585
Balancing and Memorandum Account, Beginning Balance	47,061	7,689	3,549
Balancing and Memorandum Account, Revenue Increase (Reduction), Net	24,731	41,998	5,018
Balancing and Memorandum Account, Refunds (Collections), Net	(26,586)	(2,626)	(878)
Balancing and Memorandum Account, Surcharge Offset	0	0	0
Balancing and Memorandum Account, Ending Balance	45,206	47,061	7,689
2014 WCMA [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Memorandum Account, Beginning Balance	0
Memorandum Account, Revenue Increase (Reduction)	2,981
Memorandum Account, Refunds (Collections)	(37)
Memorandum Account, Surcharge Offset	0
Memorandum Account, Ending Balance	2,944	0
2015 WCMA [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Memorandum Account, Beginning Balance	0
Memorandum Account, Revenue Increase (Reduction)	17,511
Memorandum Account, Refunds (Collections)	0
Memorandum Account, Surcharge Offset	(12,139)
Memorandum Account, Ending Balance	5,372	0
Balancing and Memorandum Account, Surcharge Offset	12,139
Water supply balancing accounts [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Balancing Account, Beginning Balance	890	(2,378)	(1,590)
Balancing Account, Revenue Increase (Reduction)	2,025	3,353	(788)
Balancing Account, Refunds (Collections)	(144)	(85)	0
Balancing Account, Surcharge Offset	0	0	0
Balancing Account, Ending Balance	2,771	890	(2,378)
Drought Surcharges [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Balancing Account, Beginning Balance	0
Balancing Account, Revenue Increase (Reduction)	0
Balancing Account, Refunds (Collections)	(12,498)
Balancing Account, Surcharge Offset	12,139
Balancing Account, Ending Balance	(359)	0
Pension Balancing Account [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Balancing Account, Beginning Balance	1,412	9,734	6,657
Balancing Account, Revenue Increase (Reduction)	(924)	(7,705)	3,077
Balancing Account, Refunds (Collections)	(1,040)	(617)	0
Balancing Account, Surcharge Offset	0	0	0
Balancing Account, Ending Balance	(552)	1,412	9,734
2012 General Rate Case True-up [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Balancing Account, Beginning Balance	44,400	0
Balancing Account, Revenue Increase (Reduction)	1,937	46,456
Balancing Account, Refunds (Collections)	(13,267)	(2,056)
Balancing Account, Surcharge Offset	0	0
Balancing Account, Ending Balance	33,070	44,400	0
Other Regulatory Assets [Member]
Schedule of Balancing and Memorandum Accounts [Line Items]
Memorandum Account, Beginning Balance	(1,377)	(1,896)	(1,887)
Memorandum Account, Revenue Increase (Reduction)	1,494	341	869
Memorandum Account, Refunds (Collections)	477	178	(878)
Memorandum Account, Surcharge Offset	0	0	0
Memorandum Account, Ending Balance	594	(1,377)	(1,896)
Balancing Account, Beginning Balance	1,736	2,229	369
Balancing Account, Revenue Increase (Reduction)	(293)	(447)	1,860
Balancing Account, Refunds (Collections)	(77)	(46)	0
Balancing Account, Surcharge Offset	0	0	0
Balancing Account, Ending Balance	$ 1,366	$ 1,736	$ 2,229

Schedule of Balancing and Memorandum Accounts [Line Items]