XML 98 R81.htm IDEA: XBRL DOCUMENT v3.8.0.1
Pension and other post-retirement benefits - Additional Information (Detail)
CAD in Thousands, $ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2017
USD ($)
Dec. 31, 2017
CAD
Dec. 31, 2017
USD ($)
Dec. 31, 2016
CAD
Dec. 31, 2017
USD ($)
Employee Benefits Disclosure [Line Items]          
Defined contribution pension plan cost   CAD 9,387   CAD 5,223  
Accumulated benefit obligation for pension plan   614,840   317,025  
Defined benefit plan, amounts recognized in other comprehensive income (loss), net prior service cost (credit) | $     $ 2,217    
Net actuarial gain (loss) for defined benefit pension plan that will be amortized from accumulated other comprehensive income over next fiscal year | $         $ 8,204
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | $ $ 2,354        
Gain on curtailment | $ $ 853        
Pension Plans          
Employee Benefits Disclosure [Line Items]          
Expected employer contributions for next year   26,686      
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)   (49,785)   (6,773)  
Gain on curtailment   (1,129)   0  
Other Postretirement Benefit Plans, Defined Benefit          
Employee Benefits Disclosure [Line Items]          
Expected employer contributions for next year   4,898      
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)   (13,321)   2,870  
Gain on curtailment   CAD (6)   CAD 0