SEGMENT REPORTING - Net Sales by Business Unit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2026	Sep. 27, 2025	Sep. 26, 2026	Sep. 27, 2025
Revenue
Total Net Sales	$ 1,732,836	$ 1,559,627	$ 5,077,040	$ 4,990,520
Corporate
Revenue
Total Net Sales	2,025	1,746	6,250	5,501
Retail \| UFP Edge
Revenue
Total Net Sales	26,631	26,140	75,404	86,765
Retail \| Operating Segments
Revenue
Total Net Sales	634,514	593,985	1,984,433	1,989,592
Retail \| Operating Segments \| Deckorators
Revenue
Total Net Sales	108,590	81,163	299,937	244,769
Retail \| Operating Segments \| ProWood
Revenue
Total Net Sales	499,293	486,682	1,609,092	1,658,058
Packaging \| Operating Segments
Revenue
Total Net Sales	465,845	394,949	1,318,183	1,233,626
Packaging \| Operating Segments \| Structural Packaging
Revenue
Total Net Sales	286,561	245,868	818,159	769,151
Packaging \| Operating Segments \| PalletOne
Revenue
Total Net Sales	155,487	126,573	433,570	402,706
Packaging \| Operating Segments \| Protective Packaging
Revenue
Total Net Sales	23,797	22,508	66,454	61,769
Construction \| Operating Segments
Revenue
Total Net Sales	552,423	496,465	1,544,713	1,563,995
Construction \| Operating Segments \| Factory Built
Revenue
Total Net Sales	218,790	201,596	627,718	648,484
Construction \| Operating Segments \| Site-Built
Revenue
Total Net Sales	187,782	168,069	525,058	561,099
Construction \| Operating Segments \| Commercial
Revenue
Total Net Sales	93,120	78,227	237,733	212,462
Construction \| Operating Segments \| Concrete Forming
Revenue
Total Net Sales	52,731	48,573	154,204	141,950
All Other \| Operating Segments
Revenue
Total Net Sales	$ 78,029	$ 72,482	$ 223,461	$ 197,806