Annual report pursuant to Section 13 and 15(d)

Income Tax - Summary of Years Open to Examination under Different Jurisdiction (Detail)

v3.8.0.1
Income Tax - Summary of Years Open to Examination under Different Jurisdiction (Detail)
 12 Months Ended
Dec. 31, 2017
Earliest Tax Year [Member] | Canada [Member] | CANADA  
Income Tax Examination [Line Items]  
Years open to examination 2009
Earliest Tax Year [Member] | Canada [Member] | UNITED KINGDOM  
Income Tax Examination [Line Items]  
Years open to examination 2010
Earliest Tax Year [Member] | US [Member]  
Income Tax Examination [Line Items]  
Years open to examination 2013
Latest Tax Year [Member] | Canada [Member] | CANADA  
Income Tax Examination [Line Items]  
Years open to examination 2017
Latest Tax Year [Member] | Canada [Member] | UNITED KINGDOM  
Income Tax Examination [Line Items]  
Years open to examination 2017
Latest Tax Year [Member] | US [Member]  
Income Tax Examination [Line Items]  
Years open to examination 2016