BUSINESS SEGMENTS (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020 USD ($)	Sep. 28, 2019 USD ($)	Sep. 26, 2020 USD ($) segment	Sep. 28, 2019 USD ($)
Business Segments
Number of reportable segments | segment			4
Net sales	$ 733,970	$ 690,340	$ 2,096,978	$ 2,083,350
Operating income	61,479	61,064	171,814	177,140
Engineered Support Structures Segment
Business Segments
Net sales	254,945	266,494	731,184	752,028
Operating income	25,434	21,825	46,183	55,152
Utility Support Structures Segment
Business Segments
Net sales	272,479	204,196	723,900	656,463
Operating income	25,881	20,362	75,255	61,443
Coatings Segment
Business Segments
Net sales	68,698	76,922	199,955	228,242
Operating income	12,416	13,865	33,618	39,037
Irrigation Segment
Business Segments
Net sales	137,848	142,728	441,939	446,617
Operating income	14,687	18,204	60,701	59,868
Sales
Business Segments
Sales	757,144	710,153	2,173,505	2,146,126
Sales | Engineered Support Structures Segment
Business Segments
Sales	255,656	268,058	739,783	757,094
Sales | Engineered Support Structures Segment | Lighting, Traffic, and Highway Safety Products
Business Segments
Sales	181,571	191,262	534,585	530,021
Sales | Engineered Support Structures Segment | Communication Products
Business Segments
Sales	50,677	48,391	139,759	138,710
Sales | Engineered Support Structures Segment | Access Systems
Business Segments
Sales	23,408	28,405	65,439	88,363
Sales | Utility Support Structures Segment
Business Segments
Sales	274,393	204,958	731,178	658,709
Sales | Utility Support Structures Segment | Steel
Business Segments
Sales	156,082	153,433	482,430	460,309
Sales | Utility Support Structures Segment | Concrete
Business Segments
Sales	39,215	28,011	120,653	88,415
Sales | Utility Support Structures Segment | Engineered Solar Tracker Solutions
Business Segments
Sales	43,287	3,418	56,830	43,642
Sales | Utility Support Structures Segment | Offshore and Other Complex Steel Structures
Business Segments
Sales	35,809	20,096	71,265	66,343
Sales | Coatings Segment
Business Segments
Sales	87,886	92,957	255,976	278,142
Sales | Irrigation Segment
Business Segments
Sales	139,209	144,180	446,568	452,181
Intersegment sales
Business Segments
Sales	23,174	19,813	76,527	62,776
Intersegment sales | Engineered Support Structures Segment
Business Segments
Sales	711	1,564	8,599	5,066
Intersegment sales | Utility Support Structures Segment
Business Segments
Sales	1,914	762	7,278	2,246
Intersegment sales | Coatings Segment
Business Segments
Sales	19,188	16,035	56,021	49,900
Intersegment sales | Irrigation Segment
Business Segments
Sales	1,361	1,452	4,629	5,564
Other
Business Segments
Operating income	(16,939)	(13,192)	(43,943)	(38,360)
North America | Sales | Irrigation Segment
Business Segments
Sales	75,803	82,840	281,397	294,127
International | Sales | Irrigation Segment
Business Segments
Sales	$ 63,406	$ 61,340	$ 165,171	$ 158,054