Segments Segments (External Customer Sales By Product) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Net sales	$ 859,521	$ 990,264	$ 998,461	$ 834,202	$ 840,881	$ 881,012	$ 886,375	$ 757,700	$ 3,682,448	$ 3,365,968	$ 3,093,743
Structural components [Member]
Revenue from External Customer [Line Items]
Net sales									622,105	522,619	461,761
Lumber & lumber sheet goods [Member]
Revenue from External Customer [Line Items]
Net sales									1,286,481	1,114,219	938,563
Millwork, Doors And Windows [Member]
Revenue from External Customer [Line Items]
Net sales									964,684	907,377	894,889
Other building products & services [Member]
Revenue from External Customer [Line Items]
Net sales									$ 809,178	$ 821,753	$ 798,530