Summary of Organization and Significant Accounting Policies - Business and Credit Concentration (Details)		9 Months Ended	12 Months Ended	21 Months Ended
	Mar. 11, 2015	Sep. 30, 2017 state item	Dec. 31, 2016 item	Sep. 30, 2017 state
Business and Credit Concentrations
Number of states in which the entity operates | state		23		23
Sales | Customer Concentration Risk
Business and Credit Concentrations
Number of customers accounted for more than 10% of total revenue		0	0
Sales | Customer Concentration Risk | Maximum
Business and Credit Concentrations
Customer accounted revenue (as a percent)		10.00%	10.00%
Summit Materials, LLC | Sales | Customer Concentration Risk
Business and Credit Concentrations
Number of customers accounted for more than 10% of total revenue		0	0
Summit Materials, LLC | Sales | Customer Concentration Risk | Maximum
Business and Credit Concentrations
Customer accounted revenue (as a percent)				10.00%
Tax Receivable Agreement
Business and Credit Concentrations
Percentage of benefits to be paid on tax receivable agreement	85.00%
Tax Receivable Agreement | Summit Holdings LP
Business and Credit Concentrations
Percentage of benefits to be paid on tax receivable agreement		85.00%