Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Gain) Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Jan. 02, 2016	Dec. 27, 2014
Amounts recognized in other comprehensive (income) loss:
Total amount recognized	$ (426)	$ (2,123)	$ 3,919
Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Total amount recognized	(426)	(2,123)	3,919
Pension Benefits
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	688	(16)	4,650
Amortization of gain	(463)	(326)	(117)
Total amount recognized	225	(342)	4,533
Pension Benefits | Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	688	(16)	4,650
Amortization of gain	(463)	(326)	(117)
Total amount recognized	225	(342)	4,533
Healthcare & Life Ins
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(682)	(1,720)	1,992
Prior service cost	64		(2,553)
Amortization of prior year service cost	174	174	174
Curtailment benefit			1,346
Amortization of gain	(207)	(235)	(227)
Total amount recognized	(651)	(1,781)	732
Healthcare & Life Ins | Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(682)	(1,720)	1,992
Prior service cost	64		(2,553)
Amortization of prior year service cost	174	174	174
Curtailment benefit			1,346
Amortization of gain	(207)	(235)	(227)
Total amount recognized	$ (651)	$ (1,781)	$ 732