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Business acquisitions (Details) $ in Thousands, $ in Thousands |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 09, 2020 USD ($) | Oct. 17, 2020 USD ($) | Oct. 13, 2020 USD ($) | Dec. 31, 2019 USD ($) MWac | Nov. 01, 2019 USD ($) | Oct. 01, 2019 USD ($) | Oct. 01, 2019 CAD ($) | Nov. 30, 2019 windProject | Mar. 04, 2021 USD ($) | Dec. 31, 2020 USD ($) MWac | Dec. 31, 2020 CAD ($) MWac | Dec. 31, 2019 USD ($) windProject MWac | Dec. 31, 2018 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  | $ 1,031,696 |  |  |  |  |  | $ 1,208,390 |  | $ 1,031,696 | $ 954,282
Non-controlling interest |  | $ (84,525) |  |  |  |  |  |  |  |  |  |  |
Number of wind projects | windProject |  |  |  |  |  |  |  |  |  |  |  | 3 |
Turquoise Solar Facility |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  | $ 20,830 |  |  |  |  |  |  |  |  |
Solar power capacity (megawatt ac) | MWac |  |  |  | 10 |  |  |  |  |  | 10 | 10 |  |
Turquoise Solar Facility | Partnership |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Partnership agreement, funded amount |  |  |  |  |  |  |  |  |  | $ 3,717 |  | $ 3,403 |
Great Bay Solar II Facility |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Solar power capacity (megawatt ac) | MWac |  |  |  |  |  |  |  |  |  | 40 | 40 |  |
Tax equity funding |  |  |  | $ 11,281 |  |  |  |  |  | $ 15,268 |  | 11,281 |
Investment tax credit |  |  |  |  |  |  |  |  |  | 10,717 |  | $ 8,526 |
North Fork Ridge Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax equity funding |  |  |  |  |  |  |  |  |  | $ 29,446 |  |  |
Empire Electric System | North Fork Ridge Wind Project | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  |  |  |  |  |  | $ 288,066 |  |  |  |
Tax equity funding |  |  |  |  |  |  |  |  | 84,926 |  |  |  |
Construction loan repaid |  |  |  |  |  |  |  |  | $ 193,506 |  |  |  |
Ascendant |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price | $ 364,468 |  |  |  |  |  |  |  |  |  |  |  |
Working capital | 71,948 |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment | 417,947 |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets | 27,315 |  |  |  |  |  |  |  |  |  |  |  |
Goodwill | 93,202 |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | 9,859 |  |  |  |  |  |  |  |  |  |  |  |
Other assets | 4,992 |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | (159,682) |  |  |  |  |  |  |  |  |  |  |  |
Pension and other post-employment benefits | (58,746) |  |  |  |  |  |  |  |  |  |  |  |
Derivative instruments | (12,748) |  |  |  |  |  |  |  |  |  |  |  |
Other liabilities | (29,619) |  |  |  |  |  |  |  |  |  |  |  |
Total net assets acquired | 364,468 |  |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents acquired | 42,920 |  |  |  |  |  |  |  |  |  |  |  |
Total net assets acquired, net of cash and cash equivalents | $ 321,548 |  |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life of assets | 29 years |  |  |  |  |  |  |  |  |  |  |  |
ESSAL |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price |  | $ 74,111 | $ 87,975 |  |  |  |  |  |  |  |  |  |
Ownership interest acquired (percent) |  | 43.00% | 51.00% |  |  |  |  |  |  |  |  |  |
Cumulative ownership interest acquired (percent) |  | 94.00% |  |  |  |  |  |  |  |  |  |  |
Working capital |  | $ 11,278 |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  | 238,504 |  |  |  |  |  |  |  |  |  |  |
Intangible assets |  | 37,095 |  |  |  |  |  |  |  |  |  |  |
Goodwill |  | 70,382 |  |  |  |  |  |  |  |  |  |  |
Other assets |  | 22 |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  | (139,534) |  |  |  |  |  |  |  |  |  |  |
Pension and other post-employment benefits |  | (2,292) |  |  |  |  |  |  |  |  |  |  |
Deferred tax liabilities, net |  | (28,074) |  |  |  |  |  |  |  |  |  |  |
Other liabilities |  | (14,881) |  |  |  |  |  |  |  |  |  |  |
Total net assets acquired |  | 87,975 |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents acquired |  | 6,983 |  |  |  |  |  |  |  |  |  |  |
Total net assets acquired, net of cash and cash equivalents |  | $ 80,992 |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life of assets |  | 40 years |  |  |  |  |  |  |  |  |  |  |
ESSAL | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest sold (percent) |  |  |  |  |  |  |  |  | 32.00% |  |  |  |
Ownership interest after transaction (percent) |  |  |  |  |  |  |  |  | 64.00% |  |  |  |
ESSAL | APUC |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Non-controlling interest (percent) |  |  |  |  |  |  |  |  |  | 6.00% |  |  |
ESSAL | Third Party | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest sold |  |  |  |  |  |  |  |  | $ 51,750 |  |  |  |
New Brunswick Gas |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  |  |  | $ 256,011 | $ 339,036 |  |  |  |  |  |
Increase (decrease) in goodwill |  |  |  |  |  |  |  |  |  | $ (1,213) | $ (1,884) |  |
St. Lawrence Gas Company, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  |  | $ 61,820 |  |  |  |  |  |  |  |
Increase (decrease) in goodwill |  |  |  |  |  |  |  |  |  | $ 3,207 |  |  |
Mid-west Wind Development Project |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Wind power capacity (megawatt AC) | MWac |  |  |  |  |  |  |  |  |  |  |  | 600 |
Southwestern Missouri Wind Projects |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of wind projects | windProject |  |  |  |  |  |  |  | 2 |  |  |  |  |

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