BUSINESS SEGMENTS (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020 USD ($)	Jun. 29, 2019 USD ($)	Jun. 27, 2020 USD ($) segment	Jun. 29, 2019 USD ($)
Business Segments
Number of reportable segments | segment			4
Net sales	$ 688,808	$ 700,871	$ 1,363,008	$ 1,393,010
Operating income	43,440	61,474	110,335	116,076
Engineered Support Structures Segment
Business Segments
Net sales	248,873	257,565	476,239	485,534
Operating income	4,818	20,882	20,749	33,327
Utility Support Structures Segment
Business Segments
Net sales	228,473	209,009	451,421	452,267
Operating income	21,650	16,033	49,374	41,081
Coatings Segment
Business Segments
Net sales	62,667	81,089	131,257	151,320
Operating income	10,148	15,032	21,202	25,172
Irrigation Segment
Business Segments
Net sales	148,795	153,208	304,091	303,889
Operating income	22,351	21,530	46,014	41,664
Sales
Business Segments
Sales	715,353	722,168	1,416,361	1,435,973
Sales | Engineered Support Structures Segment
Business Segments
Sales	253,385	258,748	484,127	489,036
Sales | Engineered Support Structures Segment | Lighting, Traffic, and Highway Safety Products
Business Segments
Sales	181,027	181,575	353,014	338,759
Sales | Engineered Support Structures Segment | Communication Products
Business Segments
Sales	50,886	47,454	89,082	90,319
Sales | Engineered Support Structures Segment | Access Systems
Business Segments
Sales	21,472	29,719	42,031	59,958
Sales | Utility Support Structures Segment
Business Segments
Sales	231,324	209,829	456,785	453,751
Sales | Utility Support Structures Segment | Steel
Business Segments
Sales	159,817	147,116	326,348	306,876
Sales | Utility Support Structures Segment | Concrete
Business Segments
Sales	45,653	30,560	81,438	60,404
Sales | Utility Support Structures Segment | Engineered Solar Tracker Solutions
Business Segments
Sales	4,619	9,932	13,543	40,224
Sales | Utility Support Structures Segment | Offshore and Other Complex Steel Structures
Business Segments
Sales	21,235	22,221	35,456	46,247
Sales | Coatings Segment
Business Segments
Sales	80,005	98,406	168,090	185,185
Sales | Irrigation Segment
Business Segments
Sales	150,639	155,185	307,359	308,001
Intersegment sales
Business Segments
Sales	26,545	21,297	53,353	42,963
Intersegment sales | Engineered Support Structures Segment
Business Segments
Sales	4,512	1,183	7,888	3,502
Intersegment sales | Utility Support Structures Segment
Business Segments
Sales	2,851	820	5,364	1,484
Intersegment sales | Coatings Segment
Business Segments
Sales	17,338	17,317	36,833	33,865
Intersegment sales | Irrigation Segment
Business Segments
Sales	1,844	1,977	3,268	4,112
Other
Business Segments
Operating income	(15,527)	(12,003)	(27,004)	(25,168)
North America | Sales | Irrigation Segment
Business Segments
Sales	99,034	102,810	205,594	211,287
International | Sales | Irrigation Segment
Business Segments
Sales	$ 51,605	$ 52,375	$ 101,765	$ 96,714