Revenue - Schedule of Disaggregation of Revenue by Product Classification (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Net Sales	$ 212.7	$ 215.7	$ 607.7	$ 631.6
ASC Topic 606
Disaggregation Of Revenue [Line Items]
Net Sales	212.7	215.7	607.7	631.6
ASC Topic 606 | Millwork Products [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	90.8	99.6	268.7	294.3
ASC Topic 606 | Building Products [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	106.1	100.4	296.1	289.7
ASC Topic 606 | Wood Products [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	$ 15.8	$ 15.7	$ 42.9	$ 47.6