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Property, plant and equipment - Schedule of Plant, Property and Equipment (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Property, Plant and Equipment [Line Items] |  |
Cost | $ 9,588,813 | $ 8,427,088
Accumulated depreciation | 1,346,975 | 1,186,108
Net book value | 8,241,838 | 7,240,980
Land |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 114,847 | 74,517
Accumulated depreciation | 0 | 0
Net book value | 114,847 | 74,517
Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 99,722 | 94,583
Accumulated depreciation | 51,979 | 47,541
Net book value | 47,743 | 47,042
Generation |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 2,918,692 | 2,816,611
Accumulated depreciation | 633,210 | 540,118
Net book value | 2,285,482 | 2,276,493
Generation | Construction in progress |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 136,424 | 140,235
Accumulated depreciation | 0 | 0
Net book value | 136,424 | 140,235
Distribution and Transmission |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 5,766,885 | 4,997,613
Accumulated depreciation | 661,786 | 598,449
Net book value | 5,105,099 | 4,399,164
Distribution and Transmission | Construction in progress |  |
Property, Plant and Equipment [Line Items] |  |
Cost | 552,243 | 303,529
Accumulated depreciation | 0 | 0
Net book value | $ 552,243 | $ 303,529

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- Definition Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(14)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(8)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(13)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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