Accounting for derivative instruments and hedging activities (Tables)

12 Months Ended

Dec. 31, 2020

Accounting for derivative instruments and hedging activities

Schedule of notional volumes of forecasted transactions

		December 31,	December 31,
	Units	2020	2019
Natural gas swaps	Natural Gas (MMBtu)	12.4	16.3
Gas purchase agreements	Natural Gas (Gigajoules)	4.0	6.4
Interest rate swaps	Interest (US$)	122.3	468.4

Schedule of fair value of derivative instruments

	December 31, 2020
	Derivative		Derivative
	Assets		Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	0.6
Interest rate swaps long-term		—		1.0
Total derivative instruments designated as cash flow hedges		—		1.6
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		4.1
Interest rate swaps long-term		—		0.9
Natural gas swaps current		—		0.8
Natural gas swaps long-term		—		1.9
Gas purchase agreements current		0.4		4.0
Gas purchase agreements long-term		—		4.3
Convertible debenture conversion option		—		1.5
Total derivative instruments not designated as cash flow hedges		0.4		17.5
Total derivative instruments	$	0.4	$	19.1

	December 31, 2019
	Derivative		Derivative
	Assets		Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	0.4
Interest rate swaps long-term		—		1.1
Total derivative instruments designated as cash flow hedges		—		1.5
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		1.9
Interest rate swaps long-term		—		1.1
Natural gas swaps current		—		1.9
Natural gas swaps long-term		—		4.2
Gas purchase agreements current		0.7		4.6
Gas purchase agreements long-term		—		9.5
Convertible debenture conversion option		—		3.2
Total derivative instruments not designated as cash flow hedges		0.7		26.4
Total derivative instruments	$	0.7	$	27.9

Schedule of changes in OCI attributable to derivative financial instruments designated as cash flow hedges

	Interest Rate
Year Ended December 31, 2020	Swaps
Accumulated OCI balance at January 1, 2020	$	1.6
Change in fair value of cash flow hedges		(0.5)
Realized from OCI during the period		0.5
Accumulated OCI balance at December 31, 2020	$	1.6
Settlements expected to be recognized from OCI in expense in the next 12 months, net of $0.1 million of tax	$	0.5
	Interest Rate
Year Ended December 31, 2019	Swaps
Accumulated OCI balance at January 1, 2019	$	1.6
Change in fair value of cash flow hedges		(0.3)
Realized from OCI during the period		0.3
Accumulated OCI balance at December 31, 2019	$	1.6

Summary of realized loss (gain) for derivative instruments not designated as cash flow hedges

	Classification of loss (gain)	Year Ended December 31,
	recognized in income	2020		2019
Gas purchase agreements	Fuel	$	8.3	$	8.2
Natural gas swaps	Fuel		2.5		0.9
Interest rate swaps	Interest, net		5.0		(3.2)

Summary of the unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments that are not designated as cash flow hedges

	Classification of gain (loss)	Year ended December 31,
	recognized in income	2020		2019
Natural gas swaps	Change in fair value of derivative instruments	$	3.4	$	(4.6)
Gas purchase agreements	Change in fair value of derivative instruments		5.4		3.2
Interest rate swaps	Change in fair value of derivative instruments		(2.0)		(7.5)
			6.8		(8.9)
Convertible debenture conversion option	Other (income) expense, net		(1.8)		1.8
Foreign currency forwards	Foreign exchange loss	$	—	$	—