Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Accumulated depreciation, depletion and amortization	$ 923,439	$ 794,251
Accumulated amortization	9,666	8,247
Valuation allowance	29,472	19,366
Summit Materials, LLC
Accumulated depreciation, depletion and amortization	923,439	794,251
Accumulated amortization	$ 9,666	$ 8,247
Class A Common Stock
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	112,275,998	111,658,927
Common stock, shares outstanding (in shares)	112,275,998	111,658,927
Class B Common Stock
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	99	99
Common stock, shares outstanding (in shares)	99	99