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Financial instruments - Additional Information (Detail) | 1 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 30, 2020 USD ($) termLoanFacility derivativeContract | Dec. 31, 2020 USD ($) $ / MWh MWh | Dec. 31, 2019 USD ($) | Dec. 31, 2020 CAD ($) $ / MWh | Jul. 17, 2020 USD ($) | Jul. 17, 2020 CAD ($) | Dec. 31, 2019 CAD ($) | Sep. 30, 2019 USD ($) instrument | May 23, 2019 USD ($)
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Number of term loan facilities | termLoanFacility | 2 |  |  |  |  |  |  |  |
Number of pay-variable and receive-fixed interest rate swaps | instrument |  |  |  |  |  |  |  | 3 |
Foreign currency gain (loss) |  | $ 28,406,000 | $ 7,795,000 |  |  |  |  |  |
Revenue collection period |  | 45 days |  |  |  |  |  |  |
Cash on hand |  | $ 101,614,000 |  |  |  |  |  |  |
Available to be drawn on senior debt facilities |  | $ 2,675,735,000 |  |  |  |  |  |  |
Accounts Receivable | Credit Concentration Risk |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Percentage of revenue contributed by large utility customers |  | 91.00% |  |  |  |  |  |  |
Ascendant |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Number of interest rate swaps redesignated as cash flow hedges | derivativeContract | 2 |  |  |  |  |  |  |  |
Liberty Power Group |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  | $ (18,875,000) | $ (15,946,000) |  |  |  |  |  |
Bonds |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, term |  |  | 10 years |  |  |  |  |  |
Senior Unsecured Notes | Senior Unsecured Notes Due January 2029 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, term |  |  | 10 years |  |  |  |  |  |
Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  | 6.20% |  |  |  | 6.20% |  |
Par value |  | 637,500,000 | $ 350,000,000 |  |  |  |  |  | $ 350,000,000
Interest rate swaps | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  |  |  |  | $ 350,000,000 |
Interest rate swaps | Bonds |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  |  |  | $ 135,000,000 |  |
Interest rate swaps | Senior Unsecured Notes |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  |  |  | $ 300,000,000 |  |
Interest rate (percent) |  |  | 4.60% |  |  |  | 4.60% |  |
Interest Rate Swap One | Ascendant |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount | $ 87,627,000 |  |  |  |  |  |  |  |
Derivative, fixed interest rate (percent) | 3.28% |  |  |  |  |  |  |  |
Interest Rate Swap Two | Ascendant |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount | $ 8,875,000 |  |  |  |  |  |  |  |
Derivative, fixed interest rate (percent) | 3.02% |  |  |  |  |  |  |  |
Currency Swap |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  | $ 650,000,000 |  |  |  |  |
Foreign currency gain (loss) |  | 13,256,000 | $ 0 |  |  |  |  |  |
Foreign exchange contract |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  | 3,581,000 | (35,277,000) |  |  |  |  |  |
Currency forward contract |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  | $ 682,500,000 | $ 923,243,000 |  |  |
Foreign currency gain on settlement of derivative |  | 2,363,000 |  |  |  |  |  |  |
Non-regulated Energy Sales |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  | 8,624,000 |  |  |  |  |  |  |
Interest expense |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  | 483,000 |  |  |  |  |  |  |
Derivative gains |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  | 1,215,000 |  |  |  |  |  |  |
Sugar Creek |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Amount reclassified from AOCI to earnings |  |  | 15,765,000 |  |  |  |  |  |
Canadian Investments and Subsidiaries |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  | $ 656,000 | $ 0 |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  | 13.64 |  | 13.64 |  |  |  |  |
Minimum | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  | 0.0825 |  | 0.0825 |  |  |  |  |
Minimum | Atlantica Yield Energy Solutions Canada, Inc | Measurement Input, Price Volatility |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  | 0.22 |  | 0.22 |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  | 98.05 |  | 98.05 |  |  |  |  |
Maximum | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  | 0.0875 |  | 0.0875 |  |  |  |  |
Maximum | Atlantica Yield Energy Solutions Canada, Inc | Measurement Input, Price Volatility |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  | 0.46 |  | 0.46 |  |  |  |  |
Weighted Average |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  | 22.96 |  | 22.96 |  |  |  |  |
Weighted Average | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  | 0.0867 |  | 0.0867 |  |  |  |  |
Cash flow hedge | Interest rate swaps |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Term of forward-starting interest rate swap |  |  | 10 years |  |  |  |  |  |
Cash flow hedge | ISO NE Spot Rate contract expiring February 2022 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Number of Megawatt hours | MWh |  | 81,408 |  |  |  |  |  |  |
Cost per Megawatt Hour | $ / MWh |  | 38.95 |  |  |  |  |  |  |

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