Income Taxes - Summary of Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Canadian statutory income tax rate	26.50%	28.30%	31.00%
Manufacturing and processing profits deduction	(0.70%)	(0.80%)	(0.60%)
Foreign rate differentials	(1.50%)	(2.00%)	(4.20%)
Losses not benefited	5.80%	11.40%	3.30%
Utilization of losses previously not benefited	(0.30%)	(10.20%)	(9.40%)
Earnings of equity accounted investees	(1.20%)	(1.60%)	(2.20%)
Investment tax credits	(2.30%)	(1.60%)	(1.30%)
Valuation allowance on deferred tax assets	(5.00%)	(6.50%)	(0.30%)
Re-measurement gains	(1.10%)	0.00%	0.00%
Other	(1.70%)	(0.40%)	(0.10%)
Effective income tax rate	18.50%	16.60%	16.20%

Effective income tax rate reconciliation deductions manufacturing and processing profits.

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Effective income tax rate reconciliation losses not benefited.

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Effective Income Tax Rate Reconciliation Remeasurement Gain

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Utilization of losses previously not benefited.

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- Definition

A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

+ References

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to changes in the valuation allowance for deferred tax assets.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the equity in earnings (losses) of unconsolidated subsidiaries that is exempt from income taxes under enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the difference between statutory income tax rates in foreign jurisdictions and the domestic federal statutory income tax rate recorded during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by investment tax credits generated or utilized under enacted tax laws during the period.

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