Segments Segments (External Customer Sales By Product) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Net sales	$ 890,564	$ 964,249	$ 946,375	$ 825,405	$ 859,521	$ 990,264	$ 998,461	$ 834,202	$ 3,626,593	$ 3,682,448	$ 3,365,968
Structural components [Member]
Revenue from External Customer [Line Items]
Net sales									636,043	622,105	522,619
Lumber & lumber sheet goods [Member]
Revenue from External Customer [Line Items]
Net sales									1,040,870	1,286,481	1,114,219
Millwork, Doors And Windows [Member]
Revenue from External Customer [Line Items]
Net sales									1,080,837	964,684	907,377
Other building products & services [Member]
Revenue from External Customer [Line Items]
Net sales									$ 868,843	$ 809,178	$ 821,753