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Commitments Narrative (Details) $ in Thousands, gal in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2016 | Dec. 31, 2018 USD ($) employee acre_foot $ / million_gallons gal | Dec. 31, 2017 USD ($) gal | Dec. 31, 2016 USD ($) gal | Dec. 31, 1997
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Purchased water |  | $ 97,378 | $ 86,456 | $ 72,971 |
Reduction in delivery schedule |  | 10.00% |  |  |
Intangible assets |  | $ 15,799 | $ 14,413 |  |
Collective Bargaining Agreement, Term of Contract | 3 years |  |  |  |
Collective bargaining agreement percent of wage increase for 2017 | 3.50% |  |  |  |
Collective bargaining agreement percent of wage increase for 2018 | 3.00% |  |  |  |
Collective bargaining agreement percent of wage increase for 2019 | 4.00% |  |  |  |
Santa Clara Valley Water District [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Master contract, negotiated term for delivery schedules |  | 3 years |  |  |
Water purchased in millions of gallons | gal |  | 19,477 | 20,172 | 18,241 |
Purchased water |  | $ 80,243 | $ 76,106 | $ 61,645 |
Minimum percent of delivery schedule to be purchased in 2017 |  | 90.00% |  |  |
Minimum volume of water to be purchased in 2017 | gal |  | 19,775 |  |  |
Cost of water to be purchased in 2017 |  | $ 84,296 |  |  |
Current contract water rate | $ / million_gallons |  | 4.3 |  |  |
Service Agreements [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Contract life of agreement with City of Cupertino |  |  |  |  | 25 years
Intangible assets |  | $ 4,128 |  |  |
Concession Fees [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Intangible assets |  | $ 6,800 | $ 6,800 |  |
SJW Group [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Number of employees | employee |  | 367 |  |  |
SJWTX,Inc. dba Canyon Lake Water Supply Corporation [Member] | Guadalupe-Blanco River Authority [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Long-term Purchase Commitment, Minimum Area Required, Next Twelve Months | acre_foot |  | 6,900 |  |  |
Notice period required for contract adjustment |  | 60 days |  |  |
SJWTX,Inc. dba Canyon Lake Water Supply Corporation [Member] | Lower Colorado River Authority [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Long-term Purchase Commitment, Minimum Area Required, Next Twelve Months | acre_foot |  | 250 |  |  |
Executive, Administrative or Supervisory Personnel [Member] | SJW Group [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Number of employees | employee |  | 132 |  |  |
Union Member [Member] | SJW Group [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Number of employees | employee |  | 235 |  |  |
Minimum [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Contract life of agreement with City of Cupertino |  | 5 years |  |  |
Maximum [Member] |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |
Contract life of agreement with City of Cupertino |  | 70 years |  |  |

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