SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Jul. 29, 2018	Sep. 28, 2019	Jul. 29, 2018
Disaggregation of Revenue [Line Items]
Total net sales	$ 1,285,043	$ 548,525	$ 3,645,332	$ 1,426,943
Commercial
Disaggregation of Revenue [Line Items]
Total net sales	464,906	548,525	1,370,152	1,426,943
Commercial | Metal building products
Disaggregation of Revenue [Line Items]
Total net sales	320,028	384,311	914,623	964,924
Commercial | Insulated metal panels
Disaggregation of Revenue [Line Items]
Total net sales	109,322	106,605	332,403	303,910
Commercial | Metal coil coating
Disaggregation of Revenue [Line Items]
Total net sales	35,556	57,609	123,126	158,109
Siding
Disaggregation of Revenue [Line Items]
Total net sales	315,799	0	840,601	0
Siding | Vinyl siding
Disaggregation of Revenue [Line Items]
Total net sales	148,912	0	400,220	0
Siding | Metal
Disaggregation of Revenue [Line Items]
Total net sales	75,933	0	199,265	0
Siding | Injection molded
Disaggregation of Revenue [Line Items]
Total net sales	17,429	0	47,163	0
Siding | Stone
Disaggregation of Revenue [Line Items]
Total net sales	32,254	0	70,441	0
Siding | Other Products and Services
Disaggregation of Revenue [Line Items]
Total net sales	41,271	0	123,512	0
Windows
Disaggregation of Revenue [Line Items]
Total net sales	504,338	0	1,434,579	0
Windows | Other Products and Services
Disaggregation of Revenue [Line Items]
Total net sales	11,283	0	39,568	0
Windows | Vinyl windows
Disaggregation of Revenue [Line Items]
Total net sales	481,104	0	1,355,333	0
Windows | Aluminum windows
Disaggregation of Revenue [Line Items]
Total net sales	$ 11,951	$ 0	$ 39,678	$ 0