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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018	Dec. 29, 2018
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 700,871	$ 682,405	$ 1,393,010	$ 1,381,089
Contract with customer, liability, current	66,128		66,128		$ 4,906
Revenue recognized from contract liability	897	1,632	1,928	4,456
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	485,581	474,740	950,432	952,025
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	215,290	207,665	442,578	429,064
Utility Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	209,009	196,531	452,267	406,390
Utility Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,932	0	40,224	0
Utility Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	199,077	196,531	412,043	406,390
Engineered Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	257,565	246,041	485,534	461,957
Engineered Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	244,604	237,720	461,074	444,914
Engineered Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,961	8,321	24,460	17,043
Coatings Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	81,089	74,539	151,320	142,997
Coatings Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	81,089	74,539	151,320	142,997
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	153,208	160,613	303,889	346,665
Irrigation Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	149,956	157,800	297,814	341,034
Irrigation Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 3,252	2,813	$ 6,075	5,631
Other Segments \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		4,681		23,080
Other Segments \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		$ 0		$ 0