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Business acquisitions and development projects - Additional Information (Details) $ in Thousands, $ in Thousands |  |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2019 USD ($) | Nov. 20, 2019 USD ($) | Jun. 03, 2019 USD ($) | May 24, 2019 USD ($) | Aug. 10, 2017 USD ($) water_utility | Dec. 31, 2019 USD ($) MW wind_project MWac | Dec. 31, 2019 CAD ($) MW wind_project MWac | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Number of wind farms | wind_project |  |  |  |  |  | 3 | 3 |  |
Mid-west Wind Development Project |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Wind power capacity (megawatt) | MW |  |  |  |  |  | 600 | 600 |  |
Total purchase price |  |  |  |  |  |  | $ 1,100,000 |  |
Ascendant Group Limited |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Total purchase price |  |  | $ 365,000 |  |  |  |  |  |
American Water Works Company |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Total purchase price |  | $ 608,000 |  |  |  |  |  |  |
Perris Water Distribution System |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  |  | $ 11,500 |  |  |  |
Number of water distribution systems acquired | water_utility |  |  |  |  | 2 |  |  |  |
Turquoise Solar Facility |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Solar power capacity (megawatt ac) | MWac |  |  |  |  |  | 10 | 10 |  |
Total purchase price | $ 20,830 |  |  |  |  |  |  |  |
Great Bay Solar Facility I |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Solar power capacity (megawatt ac) | MWac |  |  |  |  |  | 75 | 75 |  |
Great Bay Solar Facility II |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Solar power capacity (megawatt ac) | MWac |  |  |  |  |  | 40 | 40 |  |
Tax equity funding | 11,281 |  |  |  |  | $ 11,281 |  |  |
Investment tax credit |  |  |  |  |  | $ 8,526 |  |  |
Partnership | Turquoise Solar Facility |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Partnership agreement, funded amount | $ 2,000 |  |  | $ 1,403 |  |  |  |  |
Partnership | Great Bay Solar Facility I |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Partnership agreement, funded amount |  |  |  |  |  |  |  | $ 15,250 | $ 42,750

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