The average price of a hedging instrument. [Refer: Hedging instruments [member]]

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The fair value of financial assets. [Refer: At fair value [member]; Financial assets]

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The gain (loss) on hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

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The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

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Hedging instrument, energy

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Increase (decrease) through realized hedge losses recognized in cash flow hedges, equity

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Financial instruments - Natural gas forward contracts (Details) MMBTU in Thousands	12 Months Ended	36 Months Ended	48 Months Ended	108 Months Ended
	Dec. 31, 2020 USD ($) $ / MMBTU	Dec. 31, 2029 MMBTU	Jan. 01, 2025 MMBTU	Jan. 01, 2032 MMBTU	Dec. 31, 2019 USD ($) $ / MMBTU
Disclosure of financial assets [line items]
Reclassification of hedge	$ 20,271,000
Accumulated other comprehensive income
Disclosure of financial assets [line items]
Reclassification of hedge	20,271,000
Natural gas forward contract
Disclosure of financial assets [line items]
Hedging instrument, energy (in mmbtu) \| MMBTU		30	40	50
Hedge ineffectiveness	0
Natural gas forward contract \| Cash flow hedges
Disclosure of financial assets [line items]
Notional amount	1,005,600,000				$ 969,600,000
Negative fair value	$ 177,400,000				$ 195,100,000
Natural gas forward contract \| Cash flow hedges \| Geismar Facility
Disclosure of financial assets [line items]
Average contract price (in usd per mmbtu) \| $ / MMBTU	3.36				3.45
Natural gas forward contract \| Cash flow hedges \| Medicine Hat Facility
Disclosure of financial assets [line items]
Average contract price (in usd per mmbtu) \| $ / MMBTU	1.96				1.96
Natural gas forward contract \| Cash flow hedges \| other current liabilities
Disclosure of financial assets [line items]
Negative fair value	$ 14,800,000
Natural gas forward contract \| Cash flow hedges \| Other non-current liabilities
Disclosure of financial assets [line items]
Negative fair value	166,000,000.0
Natural gas forward contract \| Cash flow hedges \| other current assets
Disclosure of financial assets [line items]
Positive fair value	400,000
Natural gas forward contract \| Cash flow hedges \| Other non-current asset
Disclosure of financial assets [line items]
Positive fair value	3,000,000.0
Natural gas forward contract \| Accumulated other comprehensive income
Disclosure of financial assets [line items]
Reclassification of hedge	$ 20,300,000