Contingencies and Gain on Sale of Assets	12 Months Ended
Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies and Gain on Sale of Assets Condemnation of Properties: The laws of the State of California provide for the acquisition of public utility property by governmental agencies through their power of eminent domain, also known as condemnation, where doing so is necessary and in the public interest. In addition, these laws provide that the owner of utility property (i) may contest whether the condemnation is necessary and in the public interest, and (ii) is entitled to receive the fair market value of its property if the property is ultimately taken. Claremont System: In December 2014, the City of Claremont, California (“the City”) filed an eminent-domain action against GSWC to condemn GSWC's Claremont water system. In December 2016, the judge presiding over the eminent domain lawsuit issued a decision rejecting the City's attempt to take over GSWC's Claremont water system, and further ordered that GSWC be entitled to recover $7.6 million (“Judgment Amount”) of its litigation expenses and related defense costs from Claremont. During the first quarter of 2017, Claremont appealed both decisions. In October 2017, GSWC and the City entered into a settlement agreement whereby the City agreed to drop its appeals and in December 2017 paid $2.0 million to GSWC as partial satisfaction of the Judgment Amount, plus interest accrued through the end of 2017. GSWC recorded the $2.0 million as a reduction to legal fees of $1.8 million and an increase in interest income of $200,000 in the fourth quarter of 2017. Furthermore, under the settlement agreement, quarterly interest-only payments calculated on the unpaid Judgment Amount of $5.9 million are to be made by Claremont to GSWC through the year 2029. If Claremont (i) makes all of the quarterly payments as required, and (ii) does not take formal action to condemn GSWC's Claremont water system before December 31, 2029, then on January 1, 2030, the unpaid Judgment Amount will be deemed satisfied by Claremont without further payment required to be made to GSWC. However, if Claremont were to take formal action any time prior to December 31, 2029 or miss any of the required payments specified in the settlement agreement, the unpaid Judgment Amount and any unpaid accrued interest would immediately become due and payable. GSWC is unable to predict the actions that Claremont will take prior to December 31, 2029 and, as a result, will record the quarterly payments only to the extent that they are collected from Claremont over this period. GSWC serves approximately 11,000 customers in Claremont. Ojai Water System and Gain on Sale of Assets: In June 2017, pursuant to a settlement agreement to resolve an eminent domain action, Casitas Municipal Water District acquired the operating assets of GSWC’s 2,900-connection Ojai water system by eminent domain for $34.3 million in cash. As a result of this transaction, GSWC recorded a pretax gain of $8.3 million on the sale of the Ojai water system during the second quarter of 2017. The terms of the settlement agreement resolved the eminent domain action and dismissed all claims against GSWC brought by Casitas and another third party. Environmental Clean-Up and Remediation: GSWC has been involved in environmental remediation and cleanup at a plant site (“Chadron Plant”) that contained an underground storage tank, which was used to store gasoline for its vehicles. This tank was removed from the ground in July 1990 along with the dispenser and ancillary piping. Since then, GSWC has been involved in various remediation activities at this site. Analysis indicates that offsite monitoring wells may also be necessary to document effectiveness of remediation. As of December 31, 2018, the total spent to clean-up and remediate the Chadron Plant was approximately $5.9 million, of which $1.5 million has been paid by the State of California Underground Storage Tank Fund. Amounts paid by GSWC have been included in rate base and approved by the CPUC for recovery. As of December 31, 2018, GSWC has a regulatory asset and an accrued liability for the estimated remaining cost of $1.3 million to complete the cleanup at the site. The estimate includes costs for two years of continued activities of groundwater cleanup and monitoring, future soil treatment and site-closure-related activities. The ultimate cost may vary as there are many unknowns in remediation of underground gasoline spills and this is an estimate based on currently available information. Management also believes it is probable that the estimated additional costs will be approved in rate base by the CPUC. Other Litigation: Registrant is also subject to other ordinary routine litigation incidental to its business, some of which may include claims for compensatory and punitive damages. Management believes that rate recovery, proper insurance coverage and reserves are in place to insure against, among other things, property, general liability, employment, and workers’ compensation claims incurred in the ordinary course of business. Insurance coverage may not cover certain claims involving punitive damages. However, Registrant does not believe the outcome from any pending suits or administrative proceedings will have a material effect on Registrant's consolidated results of operations, financial position or cash flows.

Contingencies and Gain on Sale of Assets

Condemnation of Properties:

The laws of the State of California provide for the acquisition of public utility property by governmental agencies through their power of eminent domain, also known as condemnation, where doing so is necessary and in the public interest. In addition, these laws provide that the owner of utility property (i) may contest whether the condemnation is necessary and in the public interest, and (ii) is entitled to receive the fair market value of its property if the property is ultimately taken.

Claremont System:

In December 2014, the City of Claremont, California (“the City”) filed an eminent-domain action against GSWC to condemn GSWC's Claremont water system. In December 2016, the judge presiding over the eminent domain lawsuit issued a decision rejecting the City's attempt to take over GSWC's Claremont water system, and further ordered that GSWC be entitled to recover $7.6 million (“Judgment Amount”) of its litigation expenses and related defense costs from Claremont. During the first quarter of 2017, Claremont appealed both decisions.

In October 2017, GSWC and the City entered into a settlement agreement whereby the City agreed to drop its appeals and in December 2017 paid $2.0 million to GSWC as partial satisfaction of the Judgment Amount, plus interest accrued through the end of 2017. GSWC recorded the $2.0 million as a reduction to legal fees of $1.8 million and an increase in interest income of $200,000 in the fourth quarter of 2017. Furthermore, under the settlement agreement, quarterly interest-only payments calculated on the unpaid Judgment Amount of $5.9 million are to be made by Claremont to GSWC through the year 2029. If Claremont (i) makes all of the quarterly payments as required, and (ii) does not take formal action to condemn GSWC's Claremont water system before December 31, 2029, then on January 1, 2030, the unpaid Judgment Amount will be deemed satisfied by Claremont without further payment required to be made to GSWC. However, if Claremont were to take formal action any time prior to December 31, 2029 or miss any of the required payments specified in the settlement agreement, the unpaid Judgment Amount and any unpaid accrued interest would immediately become due and payable. GSWC is unable to predict the actions that Claremont will take prior to December 31, 2029 and, as a result, will record the quarterly payments only to the extent that they are collected from Claremont over this period. GSWC serves approximately 11,000 customers in Claremont.

Ojai Water System and Gain on Sale of Assets:

In June 2017, pursuant to a settlement agreement to resolve an eminent domain action, Casitas Municipal Water District acquired the operating assets of GSWC’s 2,900-connection Ojai water system by eminent domain for $34.3 million in cash. As a result of this transaction, GSWC recorded a pretax gain of $8.3 million on the sale of the Ojai water system during the second quarter of 2017. The terms of the settlement agreement resolved the eminent domain action and dismissed all claims against GSWC brought by Casitas and another third party.

Environmental Clean-Up and Remediation:

GSWC has been involved in environmental remediation and cleanup at a plant site (“Chadron Plant”) that contained an underground storage tank, which was used to store gasoline for its vehicles. This tank was removed from the ground in July 1990 along with the dispenser and ancillary piping. Since then, GSWC has been involved in various remediation activities at this site. Analysis indicates that offsite monitoring wells may also be necessary to document effectiveness of remediation.

As of December 31, 2018, the total spent to clean-up and remediate the Chadron Plant was approximately $5.9 million, of which $1.5 million has been paid by the State of California Underground Storage Tank Fund. Amounts paid by GSWC have been included in rate base and approved by the CPUC for recovery. As of December 31, 2018, GSWC has a regulatory asset and an accrued liability for the estimated remaining cost of $1.3 million to complete the cleanup at the site. The estimate includes costs for two years of continued activities of groundwater cleanup and monitoring, future soil treatment and site-closure-related activities. The ultimate cost may vary as there are many unknowns in remediation of underground gasoline spills and this is an estimate based on currently available information. Management also believes it is probable that the estimated additional costs will be approved in rate base by the CPUC.

Other Litigation:

Registrant is also subject to other ordinary routine litigation incidental to its business, some of which may include claims for compensatory and punitive damages. Management believes that rate recovery, proper insurance coverage and reserves are in place to insure against, among other things, property, general liability, employment, and workers’ compensation claims incurred in the ordinary course of business. Insurance coverage may not cover certain claims involving punitive damages. However, Registrant does not believe the outcome from any pending suits or administrative proceedings will have a material effect on Registrant's consolidated results of operations, financial position or cash flows.