SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019	Dec. 28, 2019
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 688,808	$ 700,871	$ 1,363,008	$ 1,393,010
Contract asset - costs and profits in excess of billings	125,004		125,004		$ 141,322
Contract liability - billings in excess of costs and earnings	138,820		138,820		$ 117,945
Revenue recognized from contract liability	21,037	897	39,277	1,928
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	449,101	485,581	894,236	950,432
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	239,707	215,290	468,772	442,578
Utility Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	228,473	209,009	451,421	452,267
Utility Support Structures Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4,619	9,932	13,543	40,224
Utility Support Structures Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	223,854	199,077	437,878	412,043
Engineered Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	248,873	257,565	476,239	485,534
Engineered Support Structures Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	236,827	244,604	452,706	461,074
Engineered Support Structures Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,046	12,961	23,533	24,460
Coatings Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	62,667	81,089	131,257	151,320
Coatings Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	62,667	81,089	131,257	151,320
Coatings Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Irrigation Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	148,795	153,208	304,091	303,889
Irrigation Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	144,988	149,956	296,730	297,814
Irrigation Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 3,807	$ 3,252	$ 7,361	$ 6,075