Employee Benefit Plans (Tables)

12 Months Ended

Dec. 30, 2017

Obligations and Funded Status

	2017				2016
	Pension		Healthcare		Pension		Healthcare
	benefits		& Life Ins.		benefits		& Life Ins.
Change in benefit obligations:
Beginning of period	$	27,608	$	12,770	$	27,914	$	13,458
Service cost		285		184		279		230
Interest cost		998		365		1,049		470
Actuarial loss (gain)		1,182		(338)		22		(682)
Curtailments		(430)
Change in plan provision		—		(2,325)		—		65
Benefits paid		(1,659)		(863)		(1,656)		(771)
End of period	$	27,984	$	9,793	$	27,608	$	12,770
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		863		996		771
Benefits paid		(1,659)		(863)		(1,656)		(771)
End of period	$	19,012	$	—	$	18,395	$	—
Funded status of plans	$	(8,972)	$	(9,793)	$	(9,213)	$	(12,770)
Current liabilities	$	—	$	(702)	$	—	$	(844)
Noncurrent liabilities		(8,972)		(9,091)		(9,213)		(11,926)
Liability recognized	$	(8,972)	$	(9,793)	$	(9,213)	$	(12,770)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss	$	9,341	$	2,285	$	9,248	$	3,060
Prior service cost		—		(2,413)		—		(1,968)
Total amount recognized	$	9,341	$	(128)	$	9,248	$	1,092

Amounts Recognized in Other Comprehensive (Gain) Loss

	2017				2016				2015
	Pension		Healthcare		Pension		Healthcare		Pension		Healthcare
	benefits		& Life Ins.		benefits		& Life Ins.		benefits		& Life Ins.
Amounts recognized in other comprehensive (income) loss:
Net actuarial gain (loss)	$	1,068	$	(338)	$	688	$	(682)	$	(16)	$	(1,720)
Prior service cost		—		(572)		—		64		—		—
Amortization of prior year service cost		—		168		—		174		—		174
Curtailment benefit		(429)		—		—		—		—		—
Amortization of gain		(547)		(64)		(463)		(207)		(326)		(235)
Adjustment to plan benefits		—		(414)		—		—		—		—
Total amount recognized	$	92	$	(1,220)	$	225	$	(651)	$	(342)	$	(1,781)
Components of net periodic benefit cost:
Service cost	$	285	$	184	$	279	$	230	$	159	$	149
Interest cost		998		365		1,049		470		1,041		447
Amortization of gain		547		64		463		207		326		235
Expected return on plan assets		(1,302)		—		(1,386)		—		(1,385)		—
Amortization of prior service credit		—		(168)		—		(174)		—		(174)
Net periodic benefit cost	$	528	$	445	$	405	$	733	$	141	$	657

Weighted-Average Assumptions Used to Determine Benefit Obligations

	2017		2016
		Healthcare		Healthcare
	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.
Discount rate	3.23% - 3.37%	3.20% - 3.25%	3.61% - 3.81%	3.32% - 3.65%
Expected long-term rate of return on plan assets	7.00%	N/A	7.00%	N/A

Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost

	2017		2016		2015
		Healthcare		Healthcare		Healthcare
	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.
Discount rate	3.61% - 3.81%	3.54% - 3.65%	3.74% - 3.97%	3.34% - 3.80%	3.50% - 3.98%	3.39% - 3.52%
Expected long-term rate of return on plan assets	7.00%	N/A	7.30%	N/A	7.30%	N/A

Effects of One Percentage-Point Change in Assumed Health Care Cost Trend Rates

	2017				2016
	Increase		Decrease		Increase		Decrease
Total service cost and interest cost components	$	39	$	(33)	$	55	$	(47)
APBO		857		(769)		1,197		(1,038)

Fair Value of Company's Pension Plans' Assets

	2017
			Quoted prices in active
	Total fair		markets for identical		Observable
	value		assets (Level 1)		inputs (Level 2)
Fixed income securities:
Intermediate—government	$	3,620	$	3,068	$	552
Intermediate—corporate		3,872		—		3,872
Short-term—government		497		497		—
Short-term—corporate		1,702		—		1,702
Equity securities:
U.S. Large cap value		1,765		1,765		—
U.S. Large cap growth		588		588		—
U.S. Mid cap value		586		586		—
U.S. Mid cap growth		586		586		—
U.S. Small cap value		571		571		—
U.S. Small cap growth		580		580		—
Managed Futures		392		—		392
International		1,547		677		870
Commodities Broad Basket		801		—		801
Cash		1,522		—		1,522
Precious metals		383		383		—
Total	$	19,012	$	9,301	$	9,711

	2016
			Quoted prices in active
	Total fair		markets for identical		Observable
	value		assets (Level 1)		inputs (Level 2)
Fixed income securities:
Intermediate—government	$	1,770	$	—	$	1,770
Intermediate—corporate		2,658		—		2,658
Short-term—government		912		—		912
Short-term—corporate		3,613		—		3,613
Equity securities:
U.S. Large cap value		1,181		1,181		—
U.S. Large cap growth		1,103		1,103		—
U.S. Mid cap value		577		577		—
U.S. Mid cap growth		546		546		—
U.S. Small cap value		551		551		—
U.S. Small cap growth		540		540		—
Managed Futures		366		366		—
International		1,099		1,099		—
Emerging Markets		359		359		—
Commodities Broad Basket		707		707		—
Cash		2,094		2,094		—
Precious metals		319		319		—
Total	$	18,395	$	9,442	$	8,953

Estimated Benefit Payments

	Pension		Healthcare and Life
	benefits		Insurance Benefits
2018	$	1,835	$	702
2019		1,830		667
2020		1,804		675
2021		1,771		655
2022		1,768		649
2023 - 2027		8,457		3,250

Summit Materials, LLC

Obligations and Funded Status

	2017				2016
	Pension		Healthcare		Pension		Healthcare
	benefits		& Life Ins.		benefits		& Life Ins.
Change in benefit obligations:
Beginning of period	$	27,608	$	12,770	$	27,914	$	13,458
Service cost		285		184		279		230
Interest cost		998		365		1,049		470
Actuarial loss (gain)		1,182		(338)		22		(682)
Curtailments		(430)
Change in plan provision		—		(2,325)		—		65
Benefits paid		(1,659)		(863)		(1,656)		(771)
End of period		27,984		9,793		27,608		12,770
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		863		996		771
Benefits paid		(1,659)		(863)		(1,656)		(771)
End of period		19,012		—		18,395		—
Funded status of plans	$	(8,972)	$	(9,793)	$	(9,213)	$	(12,770)
Current liabilities	$	—	$	(702)	$	—	$	(844)
Noncurrent liabilities		(8,972)		(9,091)		(9,213)		(11,926)
Liability recognized	$	(8,972)	$	(9,793)	$	(9,213)	$	(12,770)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss	$	9,341	$	2,285	$	9,248	$	3,060
Prior service cost		—		(2,413)		—		(1,968)
Total amount recognized	$	9,341	$	(128)	$	9,248	$	1,092

Amounts Recognized in Other Comprehensive (Gain) Loss

	2017				2016				2015
	Pension		Healthcare		Pension		Healthcare		Pension		Healthcare
	benefits		& Life Ins.		benefits		& Life Ins.		benefits		& Life Ins.
Amounts recognized in other comprehensive (income) loss:
Net actuarial gain (loss)	$	1,068	$	(338)	$	688	$	(682)	$	(16)	$	(1,720)
Prior service cost		—		(572)		—		64		—		—
Amortization of prior year service cost		—		168		—		174		—		174
Curtailment benefit		(429)		—		—		—		—		—
Amortization of gain		(547)		(64)		(463)		(207)		(326)		(235)
Adjustment to plan benefits		—		(414)		—		—		—		—
Total amount recognized	$	92	$	(1,220)	$	225	$	(651)	$	(342)	$	(1,781)
Components of net periodic benefit cost:
Service cost	$	285	$	184	$	279	$	230	$	159	$	149
Interest cost		998		365		1,049		470		1,041		447
Amortization of gain		547		64		463		207		326		235
Expected return on plan assets		(1,302)		—		(1,386)		—		(1,385)		—
Amortization of prior service credit		—		(168)		—		(174)		—		(174)
Net periodic benefit cost	$	528	$	445	$	405	$	733	$	141	$	657

Weighted-Average Assumptions Used to Determine Benefit Obligations

	2017		2016
		Healthcare		Healthcare
	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.
Discount rate	3.23% - 3.37%	3.20% - 3.25%	3.61% - 3.81%	3.32% - 3.65%
Expected long-term rate of return on plan assets	7.00%	N/A	7.00%	N/A

Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost

	2017		2016		2015
		Healthcare		Healthcare		Healthcare
	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.	Pension benefits	& Life Ins.
Discount rate	3.61% - 3.81%	3.54% - 3.65%	3.74% - 3.97%	3.34% - 3.80%	3.50% - 3.98%	3.39% - 3.52%
Expected long-term rate of return on plan assets	7.00%	N/A	7.30%	N/A	7.30%	N/A

Effects of One Percentage-Point Change in Assumed Health Care Cost Trend Rates

	2017				2016
	Increase		Decrease		Increase		Decrease
Total service cost and interest cost components	$	39	$	(33)	$	55	$	(47)
APBO		857		(769)		1,197		(1,038)

Fair Value of Company's Pension Plans' Assets

	2017
			Quoted prices in active
	Total fair		markets for identical		Observable
	value		assets (Level 1)		inputs (Level 2)
Fixed income securities:
Intermediate—government	$	3,620	$	3,068	$	552
Intermediate—corporate		3,872		—		3,872
Short-term—government		497		497		—
Short-term—corporate		1,702		—		1,702
Equity securities:
U.S. Large cap value		1,765		1,765		—
U.S. Large cap growth		588		588		—
U.S. Mid cap value		586		586		—
U.S. Mid cap growth		586		586		—
U.S. Small cap value		571		571		—
U.S. Small cap growth		580		580		—
Managed Futures		392		—		392
International		1,547		677		870
Commodities Broad Basket		801		—		801
Cash		1,522		—		1,522
Precious metals		383		383		—
Total	$	19,012	$	9,301	$	9,711

	2016
			Quoted prices in active
	Total fair		markets for identical		Observable
	value		assets (Level 1)		inputs (Level 2)
Fixed income securities:
Intermediate—government	$	1,770	$	—	$	1,770
Intermediate—corporate		2,658		—		2,658
Short-term—government		912		—		912
Short-term—corporate		3,613		—		3,613
Equity securities:
U.S. Large cap value		1,181		1,181		—
U.S. Large cap growth		1,103		1,103		—
U.S. Mid cap value		577		577		—
U.S. Mid cap growth		546		546		—
U.S. Small cap value		551		551		—
U.S. Small cap growth		540		540		—
Managed Futures		366		366		—
International		1,099		1,099		—
Emerging Markets		359		359		—
Commodities Broad Basket		707		707		—
Cash		2,094		2,094		—
Precious metals		319		319		—
Total	$	18,395	$	9,442	$	8,953

Estimated Benefit Payments

	Pension		Healthcare and Life
	benefits		Insurance Benefits
2018	$	1,835	$	702
2019		1,830		667
2020		1,804		675
2021		1,771		655
2022		1,768		649
2023 - 2027		8,457		3,250