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Long-term debt - Narrative (Detail) |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 17, 2018 USD ($) | Mar. 24, 2017 USD ($) Tranche | Jan. 01, 2017 USD ($) Tranche | Dec. 30, 2016 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jan. 01, 2019 CAD ($) | Jul. 25, 2018 CAD ($) | Feb. 23, 2018 USD ($) | Feb. 15, 2018 USD ($) | Dec. 21, 2017 USD ($) | Oct. 06, 2017 USD ($) | Oct. 05, 2017 CAD ($) | Sep. 20, 2017 CAD ($) | Jun. 30, 2017 USD ($) | Jan. 17, 2017 CAD ($) | Dec. 31, 2016 CAD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  | $ 321,807,000 |  |  |  |  |  |  |  |  |  |  |  |
Repayment of long-term debt |  |  |  |  |  | 1,699,592,000 | $ 2,366,105,000 |  |  |  |  |  |  |  |  |  |  |
Interest on long term debt |  |  |  |  |  | 33,822,000 | 33,064,000 |  |  |  |  |  |  |  |  |  |  |
Interest expense during the year on long-term liabilities |  |  |  |  |  | 150,262,000 | 142,791,000 |  |  |  |  |  |  |  |  |  |  |
Senior Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  | 3,336,795,000 | 3,079,551,000 |  |  |  |  |  |  |  |  |  |  |
Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Par value | $ 287,500 |  |  |  |  | $ 287,500,000 |  |  |  |  |  |  |  |  |  |  |  |
Weighted average coupon | 6.875% |  |  |  |  | 6.88% |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  | $ 278,771,000 | 0 |  |  |  |  |  |  |  |  |  |  |
Senior Unsecured Notes | Senior Unsecured Debenture Due February 2027 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  | $ 135,000,000 |  |  |  |  |  |  |  |  |
Par value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000,000 |
Maturity date |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.09% |
Debt instrument, sales price ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.99929 |
Senior Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, number of tranches | Tranche |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, weighted average life |  | 15 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Par value |  | $ 750,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average coupon |  | 4.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective weighted average interest rate |  | 3.60% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  | $ 479,000,000 |  |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility | Senior Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average coupon |  |  |  |  |  | 0.00% |  |  |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility | Senior Unsecured Notes | APUC Senior Unsecured Revolving Facility Maturing November 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 165,000,000 |  |  | $ 65,000,000
Revolving Credit Facility | Senior Unsecured Notes | Empire Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |  |
Revolving Credit Facility | Senior Unsecured Notes | Liberty Power Bilateral Revolving Credit Facility Maturing August 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000,000 | $ 350,000,000 |  |  |  |
Revolving Credit Facility | Senior Unsecured Notes | Algonquin Power Senior Unsecured Revolving Facility Maturing July 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  |  |  | $ 200,000,000 | $ 600,000,000 |  |  |  |  |  |
Amount draw on credit facility |  |  |  |  |  | $ 186,807,000 |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit | Bridge Loan | Acquisition Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount draw on credit facility |  |  |  |  |  | $ 135,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Proceed from long-term lines of credit |  |  |  | $ 1,336,440,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Senior Unsecured Notes | Senior Unsecured Notes Due January 2029 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Par value |  |  |  |  |  |  |  | $ 300,000 |  |  |  |  |  |  |  |  |  |
Weighted average coupon |  |  |  |  |  |  |  | 4.60% |  |  |  |  |  |  |  |  |  |
Debt instrument, sales price ratio |  |  |  |  |  |  |  | 0.99952 |  |  |  |  |  |  |  |  |  |
Subsequent Event | Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  | $ 135,000,000 |  |  |  |  |  |  |  |  |  |
Park Water Company | Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 63,000,000 |  |
Empire |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 907,547,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Empire | U.S. Dollar Senior Unsecured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, number of tranches | Tranche |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 102,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Empire | Secured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, number of tranches | Tranche |  |  | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 733,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of debt |  |  |  |  | $ 90,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Empire | Line of Credit | Bridge Loan | Acquisition Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceed from long-term lines of credit |  |  | $ 1,336,440,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | Senior Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, term |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | Empire | U.S. Dollar Senior Unsecured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date |  |  | 6.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | Empire | Secured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date |  |  | 3.58% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Senior Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, term |  | 30 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Empire | U.S. Dollar Senior Unsecured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date |  |  | 5.80% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Empire | Secured Utility Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date |  |  | 6.82% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Rate Reset, Period One | Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 3.677% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Rate Reset, Period Two | Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 3.927% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Rate Reset, Period Three | Senior Unsecured Notes | U.S. Dollar Subordinated Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 4.677% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount of interest payable on debt, including, but not limited to, trade payables. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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