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Property, plant and equipment - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Property, Plant, and Equipment Disclosure [Line Items] |  |
Cost of plant in service | $ 546,332 | $ 493,570
Accumulated depreciation related to commonly owned facilities | 42,476 | 8,578
Expenditures | 75,427 | 79,657
Contribution received | 6,057 | 12,742
Generation |  |
Property, Plant, and Equipment Disclosure [Line Items] |  |
Renewable generation assets related to facilities under capital lease and owned by consolidated VIE | 104,107 | 113,822
Renewable generation assets related to facilities under capital lease and owned by consolidated VIE, accumulated depreciation | 34,916 | 34,908
Depreciation expense | 1,987 | 1,633
Distribution |  |
Property, Plant, and Equipment Disclosure [Line Items] |  |
Renewable generation assets related to facilities under capital lease and owned by consolidated VIE | 1,383,960 | 1,341,716
Renewable generation assets related to facilities under capital lease and owned by consolidated VIE, accumulated depreciation | 69,960 | 28,809
Liberty Utilities Group |  |
Property, Plant, and Equipment Disclosure [Line Items] |  |
Cost of distribution assets | 3,076 | 3,076
Accumulated depreciation | 669 | $ 336
Liberty Utilities Group |  |
Property, Plant, and Equipment Disclosure [Line Items] |  |
Expansion costs | $ 1,000 |

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- Definition Capital Leased Assets and Plant Property and Equipment Owned by Consolidated VIE, Accumulated Depreciation + References No definition available. + Details
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- Definition Capital Leased Assets and Plant Property and Equipment Owned by Consolidated VIE, Gross + References No definition available. + Details
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- Definition Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84164758&loc=d3e45014-112735 + Details
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- Definition The cumulative amount of depreciation (related to long-lived, depreciable flight assets owned by the entity and used in the entity's principle business operations and capitalized assets classified as property, plant and equipment that are owned by the entity) that has been recognized in the income statement. + References No definition available. + Details
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