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Income Tax Expense and Deferred Taxes - Summary of Change in Net Deferred Tax Position (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Net deferred tax asset (liability)    
Beginning balance $ (443,501) $ (607,871)
Deferred income tax (expense) recovery related to discontinued operations   174,837
Deferred income tax liability related to Integra acquisition (126,903)  
Deferred income tax (expense) recovery in the income statement 19,849 (9,039)
Deferred tax recovery (expense) in other comprehensive income 1,428 (1,428)
Ending balance $ (549,127) $ (443,501)