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GOODWILL AND INTANGIBLE ASSETS - Impairment (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 421,679		$ 385,207
Hypothetical change in discount rate (percent)	1.00%
Goodwill impairment loss		$ 14,355
Valmont SM
Indefinite-lived Intangible Assets [Line Items]
Impairment indefinite-lived intangible assets		$ 1,425
Access Systems
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 43,400
Effect of change in discount rate on fair value of reporting unit	$ 15,000