Non-cash operating items - Changes in Non-Cash Operating Items (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure Changes In Non Cash Operating Items [Abstract]
Accounts receivable	$ (52,778)	$ (20,857)
Fuel and natural gas in storage	237	13,985
Supplies and consumables inventory	1,058	(6,028)
Income taxes recoverable	(3,440)	17,796
Prepaid expenses	(15,411)	(7,501)
Accounts payable	40,885	63,854
Accrued liabilities	(29,150)	8,872
Current income tax liability	3,818	(5,016)
Asset retirements and environmental obligations	3,562	(2,494)
Net regulatory assets and liabilities	(26,260)	(2,308)
Changes in non-cash operating items	$ (77,479)	$ 60,303

Asset Retirement And Environmental Obligations

No definition available.

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- Definition

Disclosure - Changes in Non-Cash Operating Items [Abstract]

+ References

No definition available.

+ Details

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- Definition

The increase (decrease) during the reporting period in the aggregate amount of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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- Definition

The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services.

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+ Details

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- Definition

The increase (decrease) during the reporting period in the aggregate amount of expenses incurred but not yet paid.

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+ Details

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- Definition

The increase (decrease) during the reporting period in the value of fuel held in inventory.

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+ Details

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- Definition

The increase (decrease) during the reporting period in the amounts payable to taxing authorities for taxes that are based on the reporting entity's earnings, net of amounts receivable from taxing authorities for refunds of overpayments or recoveries of income taxes, and in deferred and other tax liabilities and assets.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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- Definition

The increase (decrease) during the reporting period in income taxes receivable, which represents the amount due from tax authorities for refunds of overpayments or recoveries of income taxes paid.

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- Definition

The increase (decrease) during the period in the carrying amount of capitalized costs of materials, supplies, or both, which are not included in inventory.

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- Definition

The increase (decrease) during the reporting period of all assets and liabilities used in operating activities.

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+ Details

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- Definition

The increase (decrease) during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods.

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+ Details

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- Definition

The increase (decrease) during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the increase (decrease) of regulatory assets and liabilities combined.

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