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Employee Benefit Plans - Effects of One Percentage-Point Change in Assumed Health Care Cost Trend Rates (Detail) - USD ($)
$ in Thousands
12 Months Ended
Jan. 02, 2016
Dec. 27, 2014
Compensation and Retirement Disclosure [Abstract]    
Total service cost and interest cost components, Increase $ 45 $ 39
APBO, Increase 1,302 1,333
Total service cost and interest cost components, Decrease (36) (34)
APBO, Decrease (1,121) (1,136)
Summit Materials, LLC [Member]    
Compensation and Retirement Disclosure [Abstract]    
Total service cost and interest cost components, Increase 45 39
APBO, Increase 1,302 1,333
Total service cost and interest cost components, Decrease (36) (34)
APBO, Decrease $ (1,121) $ (1,136)