SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Apr. 29, 2018	Jun. 29, 2019	Apr. 29, 2018
Disaggregation of Revenue [Line Items]
Total net sales	$ 1,295,457	$ 457,069	$ 2,360,289	$ 878,418
Commercial
Disaggregation of Revenue [Line Items]
Total net sales	480,285	457,069	905,246	878,418
Commercial | Metal building products
Disaggregation of Revenue [Line Items]
Total net sales	321,170	304,797	594,595	580,613
Commercial | Insulated metal panels
Disaggregation of Revenue [Line Items]
Total net sales	116,709	99,792	223,081	197,305
Commercial | Metal coil coating
Disaggregation of Revenue [Line Items]
Total net sales	42,406	52,480	87,570	100,500
Siding
Disaggregation of Revenue [Line Items]
Total net sales	306,525	0	524,802	0
Siding | Vinyl siding
Disaggregation of Revenue [Line Items]
Total net sales	145,351	0	251,308	0
Siding | Metal
Disaggregation of Revenue [Line Items]
Total net sales	70,352	0	123,332	0
Siding | Injection molded
Disaggregation of Revenue [Line Items]
Total net sales	17,896	0	29,734	0
Siding | Stone
Disaggregation of Revenue [Line Items]
Total net sales	45,266	0	67,580	0
Siding | Other products
Disaggregation of Revenue [Line Items]
Total net sales	27,660	0	52,848	0
Windows
Disaggregation of Revenue [Line Items]
Total net sales	508,647	0	930,241	0
Windows | Other products
Disaggregation of Revenue [Line Items]
Total net sales	12,329	0	28,285	0
Windows | Vinyl windows
Disaggregation of Revenue [Line Items]
Total net sales	480,299	0	874,229	0
Windows | Aluminum windows
Disaggregation of Revenue [Line Items]
Total net sales	$ 16,019	$ 0	$ 27,727	$ 0