Revenue (Revenue by Product Category) (Details) - USD ($) $ in Thousands	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	$ 1,090,343	$ 964,249	$ 2,991,118	$ 2,736,029
Millwork, doors & windows [Member]
Disaggregation of Revenue [Line Items]
Net sales	299,812	285,750	883,480	796,807
Structural components [Member]
Disaggregation of Revenue [Line Items]
Net sales	185,910	175,344	510,789	483,575
Lumber & lumber sheet goods [Member]
Disaggregation of Revenue [Line Items]
Net sales	383,626	274,908	935,582	798,722
Other building products & services [Member]
Disaggregation of Revenue [Line Items]
Net sales	$ 220,995	$ 228,247	$ 661,267	$ 656,925