Employee Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Change in fair value of plan assets:
Beginning of period	$ 18,395
End of period	19,012	$ 18,395
Summit Materials, LLC
Change in benefit obligations:
Beginning of period	12,770
Service cost	184
Interest cost	365
Actuarial loss (gain)	(338)
Change in plan provision	(2,325)
Benefits paid	(863)
End of period	9,793	12,770
Change in fair value of plan assets:
Employer contributions	863
Benefits paid	(863)
Funded status of plans	(9,793)
Current liabilities	(702)
Noncurrent liabilities	(9,091)
Liability recognized	(9,793)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	2,285
Prior service cost	(2,413)
Total amount recognized	(128)
Pension Benefits
Change in benefit obligations:
Beginning of period	27,608	27,914
Service cost	285	279	$ 159
Interest cost	998	1,049	1,041
Actuarial loss (gain)	1,182	22
Curtailments	(430)
Benefits paid	(1,659)	(1,656)
End of period	27,984	27,608	27,914
Change in fair value of plan assets:
Beginning of period	18,395	18,336
Actual return on plan assets	1,415	719
Employer contributions	861	996
Benefits paid	(1,659)	(1,656)
End of period	19,012	18,395	18,336
Funded status of plans	(8,972)	(9,213)
Noncurrent liabilities	(8,972)	(9,213)
Liability recognized	(8,972)	(9,213)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	9,341	9,248
Total amount recognized	9,341	9,248
Pension Benefits | Summit Materials, LLC
Change in benefit obligations:
Beginning of period	27,608	27,914
Service cost	285	279	159
Interest cost	998	1,049	1,041
Actuarial loss (gain)	1,182	22
Curtailments	(430)
Benefits paid	(1,659)	(1,656)
End of period	27,984	27,608	27,914
Change in fair value of plan assets:
Beginning of period	18,395	18,336
Actual return on plan assets	1,415	719
Employer contributions	861	996
Benefits paid	(1,659)	(1,656)
End of period	19,012	18,395	18,336
Funded status of plans	(8,972)	(9,213)
Noncurrent liabilities	(8,972)	(9,213)
Liability recognized	(8,972)	(9,213)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	9,341	9,248
Total amount recognized	9,341	9,248
Healthcare & Life Ins
Change in benefit obligations:
Beginning of period	12,770	13,458
Service cost	184	230	149
Interest cost	365	470	447
Actuarial loss (gain)	(338)	(682)
Change in plan provision	(2,325)	65
Benefits paid	(863)	(771)
End of period	9,793	12,770	13,458
Change in fair value of plan assets:
Employer contributions	863	771
Benefits paid	(863)	(771)
Funded status of plans	(9,793)	(12,770)
Current liabilities	(702)	(844)
Noncurrent liabilities	(9,091)	(11,926)
Liability recognized	(9,793)	(12,770)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	2,285	3,060
Prior service cost	(2,413)	(1,968)
Total amount recognized	(128)	1,092
Healthcare & Life Ins | Summit Materials, LLC
Change in benefit obligations:
Beginning of period	12,770	13,458
Service cost	184	230	149
Interest cost	$ 365	470	447
Actuarial loss (gain)		(682)
Change in plan provision		65
Benefits paid		(771)
End of period		12,770	$ 13,458
Change in fair value of plan assets:
Employer contributions		771
Benefits paid		(771)
Funded status of plans		(12,770)
Current liabilities		(844)
Noncurrent liabilities		(11,926)
Liability recognized		(12,770)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss		3,060
Prior service cost		(1,968)
Total amount recognized		$ 1,092