Accounting for derivative instruments and hedging activities (Tables)

3 Months Ended

Mar. 31, 2012

Accounting for derivative instruments and hedging activities

Schedule of notional volumes of forecasted transactions

	Units	March 31, 2012		December 31, 2011
Natural gas swaps	Natural gas (Mmbtu)		12,870		14,140
Gas purchase agreements	Natural gas (GJ)		31,785		33,957
Interest rate swaps	Interest (US$)	$	51,376	$	52,711
Currency forwards	Cdn$	$	248,986	$	312,533

Schedule of fair value of derivative instruments

	March 31, 2012
	Derivative Assets		Derivative Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	1,747
Interest rate swaps long-term		—		4,627
Total derivative instruments designated as cash flow hedges		—		6,374
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		2,755
Interest rate swaps long-term		—		7,919
Foreign currency forward contracts current		10,610		—
Foreign currency forward contracts long-term		16,589		—
Natural gas swaps current		—		16,706
Natural gas swaps long-term		—		19,838
Gas purchase agreements current		—		28,960
Gas purchase agreements long-term		—		77,351
Total derivative instruments not designated as cash flow hedges		27,199		153,529
Total derivative instruments	$	27,199	$	159,903

	December 31, 2011
	Derivative Assets		Derivative Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	1,561
Interest rate swaps long-term		—		5,317
Total derivative instruments designated as cash flow hedges		—		6,878
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		2,587
Interest rate swaps long-term		—		9,637
Foreign currency forward contracts current		10,630		224
Foreign currency forward contracts long-term		22,224		221
Natural gas swaps current		—		16,439
Natural gas swaps long-term		—		18,216
Total derivative instruments not designated as cash flow hedges		32,854		47,324
Total derivative instruments	$	32,854	$	54,202

Schedule of changes in OCI attributable to derivative financial instruments

For the three month period ended March 31, 2012	Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at December 31, 2011	$	(1,704	)	$	321		$	(1,383	)
Change in fair value of cash flow hedges		15			—			15
Realized from OCI during the period		287			(57	)		230
Accumulated OCI balance at March 31, 2012	$	(1,402	)	$	264		$	(1,138	)

For the three month period ended March 31, 2011	Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at December 31, 2010	$	(427	)	$	682		$	255
Change in fair value of cash flow hedges		721			—			721
Realized from OCI during the period		(360	)		(89	)		(449	)
Accumulated OCI balance at March 31, 2011	$	(66	)	$	593		$	527

Unrealized gains and losses

Gains and losses for derivative instruments

Schedule of (gains) and losses for derivative instruments not designated as cash flow hedges

The following table summarizes realized (gains) and losses for derivative instruments not designated as cash flow hedges:

		Three months ended
	Classification of (gain) loss recognized in income	March 31, 2012			March 31, 2011
Natural gas swaps	Fuel	$	4,815		$	2,476
Gas purchase agreements	Fuel		10,829			—
Foreign currency forwards	Foreign exchange (gain) loss		(11,930	)		(2,537	)
Interest rate swaps	Interest, net		1,157			976

        The following table summarizes the unrealized gains and (losses) resulting from changes in the fair value of derivative financial instruments that are not designated as cash flow hedges:

		Three months ended
	Classification of (gain) loss recognized in income	March 31, 2012			March 31, 2011
Natural gas swaps	Change in fair value of derivatives	$	1,795		$	2,883
Gas purchase agreements	Change in fair value of derivatives		57,877			—
Interest rate swaps	Change in fair value of derivatives		(1,550	)		678
		$	58,122		$	4,239
Foreign currency forwards	Foreign exchange (gain) loss	$	5,210		$	(3,436	)