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Financial instruments - Additional Information (Detail) |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 15, 2021 CAD ($) | Nov. 30, 2020 USD ($) derivativeContract termLoanFacility | Jun. 30, 2021 USD ($) $ / MWh | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) $ / MWh MWh | Jun. 30, 2020 USD ($) | Jun. 30, 2021 CAD ($) $ / MWh | Dec. 31, 2020 USD ($) | Dec. 31, 2020 CAD ($) | Mar. 31, 2020 USD ($) | May 23, 2019 USD ($)
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of term loan facilities | termLoanFacility |  | 2 |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  |  | $ (2,995,000) | $ 8,573,000 | $ (3,268,000) | $ (28,057,000) |  |  |  |  |
Liberty Power Group |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  |  | (6,534,000) | (16,642,000) | (13,274,000) | $ 27,190,000 |  |  |  |  |
Bonds |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, term |  |  |  |  |  | 10 years |  |  |  |  |
Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Par value |  |  | 637,500,000 |  | 637,500,000 |  |  |  |  |  | $ 350,000,000
Senior Unsecured Notes | Senior Unsecured Notes Due January 2029 |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, term |  |  |  |  |  | 10 years |  |  |  |  |
Senior Unsecured Notes | Canadian Dollar Senior Unsecured Notes |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Par value |  |  | 400,000,000 |  | 400,000,000 |  | $ 1,400,669,000 |  |  |  |
Debt repaid upon maturity | $ 150,000,000 |  |  |  |  |  |  |  |  |  |
Non-regulated Energy Sales |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  |  |  |  | 1,427,000 |  |  |  |  |  |
Interest expense |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  |  |  |  | (502,000) |  |  |  |  |  |
Derivative gains |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrealized gains in AOCI to be reclassified |  |  |  |  | 1,206,000 |  |  |  |  |  |
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 |  |
Currency Swap |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  |  |  | $ 650,000,000 |  |  |  |
Foreign currency gain (loss) |  |  | 7,453,000 | 15,252,000 | 11,467,000 | $ (19,583,000) |  |  |  |  |
Currency Swap | Senior Unsecured Notes | Canadian Dollar Senior Unsecured Notes |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  |  | 2,653,000 |  |  |  |  |  |  |  |
Foreign exchange contract |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  |  | (70,000) | (1,023,000) | $ (1,991,000) | $ 3,581,000 |  |  |  |  |
Currency forward contract |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative notional amount |  |  |  |  |  |  |  | $ 682,500,000 | $ 923,243,000 |  |
Ascendant |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of interest rate swaps redesignated as cash flow hedges | derivativeContract |  | 2 |  |  |  |  |  |  |  |  |
Ascendant | Interest Rate Swap One |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative notional amount |  | $ 87,627,000 |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (percent) |  | 3.28% |  |  |  |  |  |  |  |  |
Ascendant | Interest Rate Swap Two |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative notional amount |  | $ 8,875,000 |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (percent) |  | 3.02% |  |  |  |  |  |  |  |  |
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 |  |  |  |  | 46,664 |  |  |  |  |  |
Cost per Megawatt Hour | $ / MWh |  |  |  |  | 38.95 |  |  |  |  |  |
Canadian Investments and Subsidiaries |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Foreign currency gain (loss) |  |  | $ 178,000 | $ 1,269,000 | $ 446,000 | $ (195,000) |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  |  | 14.11 |  | 14.11 |  | 14.11 |  |  |  |
Minimum | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  |  | 0.0888 |  | 0.0888 |  | 0.0888 |  |  |  |
Minimum | Atlantica Yield Energy Solutions Canada, Inc | Measurement Input, Price Volatility |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  |  | 0.22 |  | 0.22 |  | 0.22 |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  |  | 189.52 |  | 189.52 |  | 189.52 |  |  |  |
Maximum | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  |  | 0.0938 |  | 0.0938 |  | 0.0938 |  |  |  |
Maximum | Atlantica Yield Energy Solutions Canada, Inc | Measurement Input, Price Volatility |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  |  | 0.46 |  | 0.46 |  | 0.46 |  |  |  |
Weighted Average |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Forward price | $ / MWh |  |  | 26.16 |  | 26.16 |  | 26.16 |  |  |  |
Weighted Average | AYES Canada | Measurement Input, Discount Rate |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative investment, measurement input (percent) |  |  | 0.0904 |  | 0.0904 |  | 0.0904 |  |  |  |

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