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Summary of Significant Accounting Policies (Balancing and Memorandum Accounts) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2017 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Surcharge Offset |  |  | $ (7,493) | $ (16,708) | $ (12,139) |
Memorandum Account, Net1 |  |  | 11,663 | 4,357 | 8,910 | $ (1,377)
Memorandum Account, Revenue Increase (Reduction) |  |  | 19,050 | 18,863 | 21,986 |
Memorandum Account, Refunds (Collections) |  |  | (4,251) | (6,708) | 440 |
Balancing Account, Beginning Balance | $ 21,552 | $ 21,552 | 21,552 | 36,296 | 48,438 |
Balancing Account, Revenue Increase (Reduction) |  |  | 3,137 | 11,024 | 2,745 |
Balancing Account, Refunds (Collections) |  |  | (16,955) | (42,476) | (27,026) |
Balancing Account, Surcharge Offset |  |  | 8,528 | 16,708 | 12,139 |
Balancing Account, Ending Balance |  |  | 16,262 | 21,552 | 36,296 |
Balancing and Memorandum Account, Beginning Balance | 25,909 | 25,909 | 25,909 | 45,206 | 47,061 |
Balancing and Memorandum Account, Revenue Increase (Reduction), Net |  |  | 22,187 | 29,887 | 24,731 |
Balancing and Memorandum Account, Refunds (Collections), Net |  |  | (21,206) | (49,184) | (26,586) |
Balancing and Memorandum Account, Surcharge Offset |  |  | 1,035 | 0 | 0 |
Balancing and Memorandum Account, Ending Balance |  |  | 27,925 | 25,909 | 45,206 |
2017 WCMA Reserve Recorded [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Revenue Increase (Reduction) |  |  | 1,169 |  |  |
2014 WCMA [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
WCMA Reserve |  |  | 0 | 1,090 | 1,278 |
Memorandum Account, Surcharge Offset |  |  | 0 | 0 | 0 |
Memorandum Account, Net1 |  |  | 43 | 0 | 2,944 | 0
Memorandum Account, Revenue Increase (Reduction) |  |  | 1,090 | 188 | 2,981 |
Memorandum Account, Refunds (Collections) |  |  | (1,047) | (3,132) | (37) |
2015 WCMA [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
WCMA Reserve |  |  | 0 | 2,115 | 2,343 |
Memorandum Account, Surcharge Offset |  |  | 0 | 0 | (12,139) |
Memorandum Account, Net1 |  |  | 33 | 1,589 | 5,372 | 0
Memorandum Account, Revenue Increase (Reduction) |  |  | 2,101 | 211 | 17,511 |
Memorandum Account, Refunds (Collections) |  |  | (3,657) | (3,994) | 0 |
Balancing and Memorandum Account, Surcharge Offset |  |  |  |  | 12,139 |
2016 WCMA [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Surcharge Offset |  |  | (1,452) | (16,708) |  |
Memorandum Account, Net1 |  |  | 115 | 0 | 0 |
Memorandum Account, Revenue Increase (Reduction) | 1,371 |  | 1,567 | 16,708 |  |
Memorandum Account, Surcharge Offset, Increase for Interest |  |  | 196 |  |  |
Memorandum Account, Refunds (Collections) |  |  | 0 | 0 |  |
2017 WCMA [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Revenue Increase (Reduction), Gross |  |  | 13,699 |  |  |
Memorandum Account, Surcharge Offset |  |  | (6,041) |  |  |
Memorandum Account, Net1 |  |  | 6,489 | 0 |  |
Memorandum Account, Revenue Increase (Reduction) |  | 961 | 12,530 |  |  |
Memorandum Account, Refunds (Collections) |  |  | 0 |  |  |
2017 WCMA Post Drought Surcharges [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Revenue Increase (Reduction) |  |  | 7,658 |  |  |
Water supply balancing accounts [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Balancing Account, Beginning Balance | 5,190 | 5,190 | 5,190 | 2,771 | 890 |
Balancing Account, Revenue Increase (Reduction) |  |  | 2,921 | 1,620 | 2,025 |
Balancing Account, Refunds (Collections) |  |  | 568 | 799 | (144) |
Balancing Account, Surcharge Offset |  |  | 0 | 0 | 0 |
Balancing Account, Ending Balance |  |  | 8,679 | 5,190 | 2,771 |
Drought Surcharges [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Balancing Account, Beginning Balance | (7,688) | (7,688) | (7,688) | (359) | 0 |
Balancing Account, Revenue Increase (Reduction) |  |  | 0 | 0 | 0 |
Balancing Account, Refunds (Collections) |  |  | (765) | (24,037) | (12,498) |
Balancing Account, Surcharge Offset |  |  | 8,453 | 16,708 | 12,139 |
Balancing Account, Ending Balance |  |  | 0 | (7,688) | (359) |
Pension Balancing Account [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Balancing Account, Beginning Balance | (2,009) | (2,009) | (2,009) | (552) | 1,412 |
Balancing Account, Revenue Increase (Reduction) |  |  | 894 | 1,120 | (924) |
Balancing Account, Refunds (Collections) |  |  | (1,344) | (2,577) | (1,040) |
Balancing Account, Surcharge Offset |  |  | 0 | 0 | 0 |
Balancing Account, Ending Balance |  |  | (2,459) | (2,009) | (552) |
2012 General Rate Case True-up [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Balancing Account, Beginning Balance | 20,682 | 20,682 | 20,682 | 33,070 | 44,400 |
Balancing Account, Revenue Increase (Reduction) |  |  | 0 | 0 | 1,937 |
Balancing Account, Refunds (Collections) |  |  | (9,363) | (12,388) | (13,267) |
Balancing Account, Surcharge Offset |  |  | 0 | 0 | 0 |
Balancing Account, Ending Balance |  |  | 11,319 | 20,682 | 33,070 |
2015 General Rate Case True-up [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Balancing Account, Beginning Balance | 5,528 | 5,528 | 5,528 | 0 |  |
Balancing Account, Revenue Increase (Reduction) |  |  | 0 | 8,767 |  |
Balancing Account, Refunds (Collections) |  |  | (5,413) | (3,239) |  |
Balancing Account, Surcharge Offset |  |  | 0 | 0 |  |
Balancing Account, Ending Balance |  |  | 115 | 5,528 | 0 |
Other Regulatory Assets [Member] |  |  |  |  |  |
Schedule of Balancing and Memorandum Accounts [Line Items] |  |  |  |  |  |
Memorandum Account, Surcharge Offset |  |  | 0 | 0 | 0 |
Memorandum Account, Net1 |  |  | 4,983 | 2,768 | 594 | $ (1,377)
Memorandum Account, Revenue Increase (Reduction) |  |  | 1,762 | 1,756 | 1,494 |
Memorandum Account, Refunds (Collections) |  |  | 453 | 418 | 477 |
Balancing Account, Beginning Balance | $ (151) | $ (151) | (151) | 1,366 | 1,736 |
Balancing Account, Revenue Increase (Reduction) |  |  | (678) | (483) | (293) |
Balancing Account, Refunds (Collections) |  |  | (638) | (1,034) | (77) |
Balancing Account, Surcharge Offset |  |  | 75 | 0 | 0 |
Balancing Account, Ending Balance |  |  | $ (1,392) | $ (151) | $ 1,366 |

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- Definition This represents the under-collection or over-collection associated with expense changes and the revenue authorized by the CPUC to offset those expense changes. Pursuant to Section 792.5 of the California Public Utilities Code, a balancing account must be maintained for expense items for which revenue offsets have been authorized. Since the amounts in the balancing accounts must be approved by the CPUC before they can be incorporated into rates, the Company does not recognize balancing accounts in its revenue until CPUC approval occurs. It is typical for the CPUC to incorporate any over-collected and/or under-collected balances in balancing accounts into customer rates at the time rate decisions are made as part of the Company’s general rate case proceedings by assessing temporary surcredits and/or surcharges. + References No definition available. + Details
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