SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 26, 2020	Sep. 26, 2020	Jun. 27, 2020	Mar. 28, 2020	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales	$ 798,377	$ 733,970	$ 688,808	$ 674,200	$ 683,626	$ 690,340	$ 700,871	$ 692,139	$ 2,895,355	$ 2,766,976	$ 2,757,144
Contract assets	123,495				141,322				123,495	141,322
Contract liabilities	170,919				117,945				170,919	117,945
Contract liabilities, current	130,018				$ 117,945				130,018	117,945
Revenue recognized from contract liability									74,319	3,921
Remaining performance obligation	39,000								39,000
Contract Liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract liabilities, current	130,018								130,018
Other Noncurrent Liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract liabilities, noncurrent	$ 40,901								40,901
Utility Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									1,002,138	885,608	855,206
Engineered Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									983,523	1,002,076	967,358
Coatings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales										300,640	286,739
Irrigation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									640,092	578,652	624,761
Point in Time
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									1,921,328	1,865,064	1,861,641
Point in Time | Utility Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									86,382	47,450	16,760
Point in Time | Engineered Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									940,513	952,056	922,677
Point in Time | Coatings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									269,602	300,640	286,739
Point in Time | Irrigation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									624,831	564,918	612,385
Point in Time | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									0	0	23,080
Over Time
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									974,027	901,912	895,503
Over Time | Utility Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									915,756	838,158	838,446
Over Time | Engineered Support Structures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									43,010	50,020	44,681
Over Time | Coatings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									0	0	0
Over Time | Irrigation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									15,261	13,734	12,376
Over Time | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales									$ 0	$ 0	$ 0
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of performance obligation satisfaction	12 months								12 months
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of performance obligation satisfaction	24 months								24 months