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Financial instruments - Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Fair Value of Financial Instruments [Line Items] |  |
Other long-term investments | $ 34,362 | $ 37,271
Cross currency swap | Net Investment Hedging |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 93,198 |
Foreign exchange forward | Net Investment Hedging |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 0 |
Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 1,171 |
Interest rate swaps |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 8,473 |
Level 1 |  |
Fair Value of Financial Instruments [Line Items] |  |
Other long-term investments | 814,530 |
Total financial assets | 814,530 |
Long-term debt | 768,400 | 651,969
Convertible debentures | 639 | 1,018
Total financial liabilities | 769,039 | 652,987
Level 2 |  |
Fair Value of Financial Instruments [Line Items] |  |
Notes receivable | 110,019 | 38,192
Derivative financial instruments, assets | 970 | 183
Total financial assets | 110,989 | 38,375
Long-term debt | 2,588,373 | 2,610,742
Convertible debentures | 0 |
Derivative financial instruments, liabilities | 102,785 | 68,867
Total financial liabilities | 2,704,861 | 2,694,733
Level 2 | Energy contracts | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets |  | 109
Level 2 | Energy contracts | Not designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities |  | 31
Level 2 | Cross currency swap | Designated as a hedge | Net Investment Hedging |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 93,198 | 57,412
Level 2 | Foreign exchange forward | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 869 |
Level 2 | Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 101 | 74
Derivative financial instruments, liabilities | 1,114 | 2,620
Level 2 | Interest rate swaps | Designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 8,473 | 8,460
Level 2 | Interest rate swaps | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities |  | 344
Level 2 | Series C Preferred Stock |  |
Fair Value of Financial Instruments [Line Items] |  |
Convertible debentures |  | 15,124
Preferred shares, Series C | 13,703 |
Level 3 |  |
Fair Value of Financial Instruments [Line Items] |  |
Notes receivable | 0 | 0
Derivative financial instruments, assets | 61,838 | 63,363
Total financial assets | 61,838 | 63,363
Derivative financial instruments, liabilities | 57 | 77
Total financial liabilities | 57 | 77
Level 3 | Energy contracts | Designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 61,838 | 63,363
Derivative financial instruments, liabilities | 57 | 77
Level 3 | Energy contracts | Not designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets |  | 0
Level 3 | Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 0 |
Portion at Other than Fair Value Measurement [Member] | Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets |  | 441
Carrying amount |  |
Fair Value of Financial Instruments [Line Items] |  |
Notes receivable | 103,696 | 33,378
Other long-term investments | 814,530 |
Derivative financial instruments, assets | 62,808 | 63,546
Total financial assets | 981,034 | 96,924
Long-term debt | 3,336,795 | 3,079,551
Convertible debentures | 470 | 971
Derivative financial instruments, liabilities | 102,842 | 68,944
Total financial liabilities | 3,453,525 | 3,164,184
Carrying amount | Energy contracts | Designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 61,838 | 63,363
Derivative financial instruments, liabilities | 57 | 77
Carrying amount | Energy contracts | Not designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets |  | 109
Derivative financial instruments, liabilities |  | 31
Carrying amount | Cross currency swap | Designated as a hedge | Net Investment Hedging |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 93,198 | 57,412
Carrying amount | Foreign exchange forward | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 869 |
Carrying amount | Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 101 | 74
Derivative financial instruments, liabilities | 1,114 | 2,620
Carrying amount | Interest rate swaps | Designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 8,473 | 8,460
Carrying amount | Interest rate swaps | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities |  | 344
Carrying amount | Series C Preferred Stock |  |
Fair Value of Financial Instruments [Line Items] |  |
Convertible debentures |  | 14,718
Preferred shares, Series C | 13,418 |
Fair value |  |
Fair Value of Financial Instruments [Line Items] |  |
Notes receivable | 110,019 | 38,192
Other long-term investments | 814,530 |
Derivative financial instruments, assets | 62,808 | 63,546
Total financial assets | 987,357 | 101,738
Long-term debt | 3,356,773 | 3,262,711
Convertible debentures | 639 | 1,018
Derivative financial instruments, liabilities | 102,842 | 68,944
Total financial liabilities | 3,473,957 | 3,347,797
Fair value | Energy contracts | Designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 61,838 | 63,363
Derivative financial instruments, liabilities | 57 | 77
Fair value | Energy contracts | Not designated as a hedge | Cash flow hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets |  | 109
Derivative financial instruments, liabilities |  | 31
Fair value | Cross currency swap | Designated as a hedge | Net Investment Hedging |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 93,198 | 57,412
Fair value | Foreign exchange forward | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 869 |
Fair value | Commodity contracts for regulatory operations |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, assets | 101 | 74
Derivative financial instruments, liabilities | 1,114 | 2,620
Fair value | Interest rate swaps | Designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities | 8,473 | 8,460
Fair value | Interest rate swaps | Not designated as a hedge |  |
Fair Value of Financial Instruments [Line Items] |  |
Derivative financial instruments, liabilities |  | 344
Fair value | Series C Preferred Stock |  |
Fair Value of Financial Instruments [Line Items] |  |
Convertible debentures |  | $ 15,124
Preferred shares, Series C | $ 13,703 |

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock. + References No definition available. + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313 + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle). + 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 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Fair value portion of shares that an entity is required to redeem for cash or other assets at a fixed or determinable date or upon the occurrence of an event. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 25 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6939902&loc=d3e21216-110875 + Details
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