RESTRUCTURING - Summary of Severance Liability and Cash Payments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Apr. 03, 2021	Dec. 31, 2020	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 3,562	$ 2,663	$ 2,418
Costs incurred	1,322	26,573	9,658
Cash payments	(1,918)	(25,674)	(9,413)
Restructuring reserve, ending balance	2,966	3,562	2,663
Corporate
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	430	1,763	2,333
Costs incurred	73	3,013	4,009
Cash payments	(73)	(4,346)	(4,579)
Restructuring reserve, ending balance	430	430	1,763
Windows | Operating Segments
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	306	418	0
Costs incurred	651	4,294	1,094
Cash payments	(427)	(4,406)	(676)
Restructuring reserve, ending balance	530	306	418
Siding | Operating Segments
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	835	482	85
Costs incurred	118	2,705	1,834
Cash payments	(644)	(2,352)	(1,437)
Restructuring reserve, ending balance	309	835	482
Commercial | Operating Segments
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	1,991	0	0
Costs incurred	480	16,561	2,721
Cash payments	(774)	(14,570)	(2,721)
Restructuring reserve, ending balance	$ 1,697	$ 1,991	$ 0