Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Gain) Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	$ (1,209)	$ (605)
Curtailment benefit		(309)
Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(1,661)	(699)	$ 688
Prior service cost			0
Amortization of prior year service cost			0
Curtailment benefit		(429)	0
Amortization of gain			(463)
Adjustment to plan benefits			0
Total amount recognized			225
Pension Benefits
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(1,300)	1,068	688
Prior service cost	0	0	0
Amortization of prior year service cost	0	0	0
Curtailment benefit	0	(429)	0
Amortization of gain	(312)	(547)	(463)
Adjustment to plan benefits	0	0	0
Total amount recognized	(1,612)	92	225
Pension Benefits | Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(1,300)	1,068
Prior service cost	0	0
Amortization of prior year service cost	0	0
Curtailment benefit	0	(429)
Amortization of gain	(312)	(547)
Adjustment to plan benefits	0	0
Total amount recognized	(1,612)	92
Healthcare & Life Ins
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(172)	(338)	(682)
Prior service cost	0	(572)	64
Amortization of prior year service cost	241	168	174
Curtailment benefit	0	0	0
Amortization of gain	(118)	(64)	(207)
Adjustment to plan benefits	0	(414)	0
Total amount recognized	(49)	(1,220)	(651)
Healthcare & Life Ins | Summit Materials, LLC
Amounts recognized in other comprehensive (income) loss:
Net actuarial (loss) gain	(172)	(338)	(682)
Prior service cost	0	(572)	64
Amortization of prior year service cost	241	168	174
Curtailment benefit	0	0	0
Amortization of gain	(118)	(64)	(207)
Adjustment to plan benefits	0	(414)	0
Total amount recognized	$ (49)	$ (1,220)	$ (651)