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Regulatory matters - Regulatory Assets and Liabilities (Detail) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | $ 446,723 | $ 450,474
Less: current regulatory assets | (42,398) | (59,037)
Non-current regulatory assets | 404,325 | 391,437
Total regulatory liabilities | 581,897 | 578,592
Less: current regulatory liabilities | (38,880) | (39,005)
Non-current regulatory liabilities | 543,017 | 539,587
Taxes |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 322,290 | 323,384
Cost of removal |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 196,469 | 193,564
Rate-base offset |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 9,778 | 10,900
Fuel and commodity costs adjustment |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 19,715 | 22,552
Deferred compensation received in relation to lost production |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 4,788 | 6,003
Deferred construction costs - fuel related |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 7,178 | 7,258
Pension and post-employment benefits |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 6,519 | 2,170
Other |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory liabilities | 15,160 | 12,761
Environmental remediation |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 83,903 | 82,295
Pension and post-employment benefits |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 125,412 | 125,959
Debt premium |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 45,499 | 48,847
Fuel and commodity costs adjustment |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 21,283 | 26,310
Rate adjustment |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 33,516 | 37,202
Clean Energy and other customer programs |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 24,330 | 22,269
Deferred construction costs - fuel related |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 13,807 | 13,986
Asset retirement |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 22,529 | 21,048
Taxes |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 34,971 | 34,822
Rate case costs |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | 8,040 | 7,990
Other |  |
Regulatory Assets And Liabilities [Line Items] |  |
Total regulatory assets | $ 33,433 | $ 29,746

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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