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Summary of Significant Accounting Policies (Balancing and Memorandum Accounts) (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Dec. 28, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | $ 21,705,000 |  |
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 3,827,000 |  |
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 17,000 |  |
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | $ 0 | $ 0
Revenue Accounts, Ending Balance |  | 25,549,000 | 21,705,000 |
Cost-recovery Accounts, Beginning Balance |  | 6,220,000 |  |
Balancing and Memorandum Cost Recovery Account, Increase (Decrease) |  | 2,643,000 |  |
Balancing and Memorandum Cost Recovery Account, Refunds (Collections) |  | 1,000 |  |
Balancing and Memorandum Cost Recovery Account, Surcharge Offset |  | 0 |  |
Cost-recovery Accounts, Ending Balance |  | 8,864,000 | 6,220,000 |
Balancing and Memorandum Account, Beginning Balance |  | 27,925,000 | 25,909,000 | 45,206,000
Balancing and Memorandum Account, Increase (Decrease) |  | 6,470,000 | 22,187,000 | 29,887,000
Balancing and Memorandum Account, Refunds (Collections), Net |  | 18,000 | (21,206,000) | (49,184,000)
Balancing and Memorandum Account, Surcharge Offset |  | 0 | 1,035,000 | 0
Balancing and Memorandum Account, Ending Balance |  | 34,413,000 | 27,925,000 | 25,909,000
Regulatory Balancing and Memorandum Accounts, Net Under-Collected |  | $ 1,573,000 |  |
Approved Balancing and Memorandum Accounts, Net | $ 27,045,000 |  |  |
Authorized Regulatory Surcharge, Net | $ 0.5894 |  |  |
Regulatory Balancing and Memorandum Accounts Review, Authorized Revenue, Threshold Percentage |  | 2.00% |  |
Cost-Recovery Accounts [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | $ 6,220,000 | 3,181,000 | 2,219,000
Balancing and Memorandum Revenue Account, Increase (Decrease) |  |  | 3,815,000 | 2,740,000
Balancing and Memorandum Revenue Account, Refunds (Collections) |  |  | (776,000) | (1,778,000)
Revenue Accounts, Ending Balance |  |  | 6,220,000 | 3,181,000
2017 WCMA Reserve Recorded [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Memorandum Account, Revenue Increase (Reduction) |  | 0 | (1,169,000) |
2014-2016 WCMA [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 191,000 | 1,589,000 | 8,316,000
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | (116,000) | 4,758,000 | 17,107,000
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 4,000 | (4,704,000) | (7,126,000)
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | (1,452,000) | (16,708,000)
Revenue Accounts, Ending Balance |  | 79,000 | 191,000 | 1,589,000
Water supply balancing accounts [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Cost-recovery Accounts, Beginning Balance |  | 8,679,000 |  |
Balancing and Memorandum Cost Recovery Account, Increase (Decrease) |  | 939,000 |  |
Balancing and Memorandum Cost Recovery Account, Refunds (Collections) |  | (1,000) |  |
Balancing and Memorandum Cost Recovery Account, Surcharge Offset |  | 0 |  |
Cost-recovery Accounts, Ending Balance |  | 9,617,000 | 8,679,000 |
Drought Surcharges [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 0 | (7,688,000) | (359,000)
Balancing and Memorandum Revenue Account, Increase (Decrease) |  |  | 0 | 0
Balancing and Memorandum Revenue Account, Refunds (Collections) |  |  | (765,000) | (24,037,000)
Balancing and Memorandum Revenue Account, Surcharge Offset |  |  | 8,453,000 | 16,708,000
Revenue Accounts, Ending Balance |  |  | 0 | (7,688,000)
Pension Balancing Account [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Cost-recovery Accounts, Beginning Balance |  | (2,459,000) |  |
Balancing and Memorandum Cost Recovery Account, Increase (Decrease) |  | 614,000 |  |
Balancing and Memorandum Cost Recovery Account, Refunds (Collections) |  | 2,000 |  |
Balancing and Memorandum Cost Recovery Account, Surcharge Offset |  | 0 |  |
Cost-recovery Accounts, Ending Balance |  | (1,843,000) | (2,459,000) |
2012 General Rate Case True-up [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 11,319,000 | 20,682,000 | 33,070,000
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 0 | 0 | 0
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 9,000 | (9,363,000) | (12,388,000)
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | 0 | 0
Revenue Accounts, Ending Balance |  | 11,328,000 | 11,319,000 | 20,682,000
2015 General Rate Case True-up [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 115,000 | 5,528,000 | 0
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 0 | 0 | 8,767,000
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 3,000 | (5,413,000) | (3,239,000)
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | 0 | 0
Revenue Accounts, Ending Balance |  | 118,000 | 115,000 | 5,528,000
Cost of capital [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | (144,000) | (817,000) | (1,440,000)
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | (1,379,000) | 0 | 3,000
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 0 | 673,000 | 620,000
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | 0 | 0
Revenue Accounts, Ending Balance |  | (1,523,000) | (144,000) | (817,000)
Other Regulatory Assets [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 3,735,000 | 3,434,000 | 3,400,000
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 1,258,000 | 1,084,000 | 1,270,000
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 1,000 | (858,000) | (1,236,000)
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | 75,000 | 0
Revenue Accounts, Ending Balance |  | 4,994,000 | 3,735,000 | 3,434,000
Cost-recovery Accounts, Beginning Balance |  | 0 |  |
Balancing and Memorandum Cost Recovery Account, Increase (Decrease) |  | 1,090,000 |  |
Balancing and Memorandum Cost Recovery Account, Refunds (Collections) |  | 0 |  |
Balancing and Memorandum Cost Recovery Account, Surcharge Offset |  | 0 |  |
Cost-recovery Accounts, Ending Balance |  | 1,090,000 | 0 |
2017 WCMA [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Memorandum Account, Revenue Increase (Reduction), Gross |  | 1,182,000 |  |
Revenue Accounts, Beginning Balance |  | 6,489,000 | 0 |
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 1,182,000 | 12,530,000 |
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 0 | 0 |
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 | (6,041,000) |
Revenue Accounts, Ending Balance |  | 7,671,000 | 6,489,000 | $ 0
2018 WCMA [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Memorandum Account, Revenue Increase (Reduction) |  | (9,386,000) |  |
Revenue Accounts, Beginning Balance |  | 0 |  |
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | 9,386,000 |  |
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 0 |  |
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 |  |
Revenue Accounts, Ending Balance |  | 9,386,000 | 0 |
2018 WCMA Reserve Recorded [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Memorandum Account, Revenue Increase (Reduction) |  | 0 |  |
Tax memorandum [Member] |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |
Revenue Accounts, Beginning Balance |  | 0 |  |
Balancing and Memorandum Revenue Account, Increase (Decrease) |  | (6,504,000) |  |
Balancing and Memorandum Revenue Account, Refunds (Collections) |  | 0 |  |
Balancing and Memorandum Revenue Account, Surcharge Offset |  | 0 |  |
Revenue Accounts, Ending Balance |  | $ (6,504,000) | $ 0 |

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