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Summary of Significant Accounting Policies - Real Estate Investments (Details) $ in Thousands |  |  |  | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 28, 2020 USD ($) entity | Dec. 19, 2019 USD ($) | Apr. 22, 2019 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Land |  |  |  | $ 14,168 | $ 14,168 |
Buildings and improvements |  |  |  | 43,961 | 43,531 |
Total real estate investment |  |  |  | 58,129 | 57,699 |
Proceeds from sale of real estate held-for-investment |  |  | $ 745 |  |  |
Gain on sale of real estate investments |  |  |  | 948 | 929 | $ 0
Operating Leases, Future Minimum Payments Receivable [Abstract] |  |  |  |  |  |
2021 |  |  |  | 4,264 |  |
2022 |  |  |  | 2,745 |  |
2023 |  |  |  | 2,565 |  |
2024 |  |  |  | 2,645 |  |
2025 |  |  |  | 2,833 |  |
Thereafter |  |  |  | 7,711 |  |
Land and Building |  |  |  |  |  |
Assets Leased or Available for Lease [Abstract] |  |  |  |  |  |
Assets leased or available for lease |  |  |  | 57,273 | $ 56,839 |
Connecticut Water Company |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Gain on sale of real estate investments |  | $ 4 |  |  |  |
Maine Water Company |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Proceeds from sale of real estate held-for-investment |  | 600 |  | 143 |  |
Gain on sale of real estate investments |  | 180 |  | (100) |  |
Selling expense |  |  |  | $ 45 |  |
Conservation easement, value |  | 1,200 |  |  |  |
Contribution of property |  | $ 600 |  |  |  |
Parent |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Gain on sale of real estate investments |  |  | 521 |  |  |
Noncontrolling Interest |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Gain on sale of real estate investments |  |  | $ 224 |  |  |
San Jose Water Company |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Sale Of Real Estate Held-For-Investment, Number Of Nonutility Properties | entity | 6 |  |  |  |  |
Proceeds from sale of real estate held-for-investment | $ 1,075 |  |  |  |  |
Gain on sale of real estate investments | 1,048 |  |  |  |  |
Selling expense | $ 22 |  |  |  |  |
Building and Building Improvements | Minimum |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Estimated useful life |  |  |  | 7 years |  |
Building and Building Improvements | Maximum |  |  |  |  |  |
Components of Real Estate Investments [Abstract] |  |  |  |  |  |
Estimated useful life |  |  |  | 39 years |  |

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