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Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Gain) Loss (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 30, 2017
Dec. 31, 2016
Jan. 02, 2016
Amounts recognized in other comprehensive (income) loss:      
Actuarial loss (credit) expected to be amortized from AOCI $ 300    
Prior Service cost (credit) expected to be amortized from AOCI (200)    
Pension Benefits      
Amounts recognized in other comprehensive (income) loss:      
Net actuarial (loss) gain 1,068 $ 688 $ (16)
Curtailment benefit (429)    
Amortization of gain (547) (463) (326)
Total amount recognized 92 225 (342)
Pension Benefits | Summit Materials, LLC      
Amounts recognized in other comprehensive (income) loss:      
Net actuarial (loss) gain 1,068 688 (16)
Curtailment benefit (429)    
Amortization of gain (547) (463) (326)
Total amount recognized 92 225 (342)
Healthcare & Life Ins      
Amounts recognized in other comprehensive (income) loss:      
Net actuarial (loss) gain (338) (682) (1,720)
Prior service cost (572) 64  
Amortization of prior year service cost 168 174 174
Amortization of gain (64) (207) (235)
Adjustment to plan benefits (414)    
Total amount recognized (1,220) (651) (1,781)
Healthcare & Life Ins | Summit Materials, LLC      
Amounts recognized in other comprehensive (income) loss:      
Net actuarial (loss) gain (338) (682) (1,720)
Prior service cost (572) 64  
Amortization of prior year service cost 168 174 174
Amortization of gain (64) (207) (235)
Adjustment to plan benefits (414)    
Total amount recognized $ (1,220) $ (651) $ (1,781)