GOODWILL AND INTANGIBLE ASSETS - Carrying Amount of Goodwill (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 25, 2021	Dec. 25, 2021	Dec. 26, 2020	Dec. 28, 2019
Goodwill [Line Items]
Goodwill, Gross			$ 492,144,000	$ 478,111,000
Accumulated impairment losses			(61,822,000)	(49,247,000)
Carrying amount of goodwill
Balance at the beginning of the period		$ 430,322,000	428,864,000
Acquisitions		284,253,000	6,138,000
Impairment	$ 0		(12,575,000)
Foreign currency translation		(6,009,000)	7,895,000
Balance at the end of the period		708,566,000	430,322,000
Engineered Support Structures Segment
Goodwill [Line Items]
Goodwill, Gross			232,323,000	228,634,000
Accumulated impairment losses			(31,245,000)	(18,670,000)
Carrying amount of goodwill
Balance at the beginning of the period		201,078,000	209,964,000
Acquisitions		0	0
Impairment			(12,575,000)
Foreign currency translation		(1,632,000)	3,689,000
Balance at the end of the period		199,446,000	201,078,000
Utility Support Structures Segment
Goodwill [Line Items]
Goodwill, Gross			135,335,000	130,594,000
Accumulated impairment losses			(14,355,000)	(14,355,000)
Carrying amount of goodwill
Balance at the beginning of the period		120,980,000	116,239,000
Acquisitions		0	1,100,000
Impairment			0
Foreign currency translation		(3,256,000)	3,641,000
Balance at the end of the period		117,724,000	120,980,000
Coatings Segment
Goodwill [Line Items]
Goodwill, Gross			94,309,000	93,747,000
Accumulated impairment losses			(16,222,000)	(16,222,000)
Carrying amount of goodwill
Balance at the beginning of the period		78,087,000	77,525,000
Acquisitions		0	0
Impairment			0
Foreign currency translation		(203,000)	562,000
Balance at the end of the period		77,884,000	78,087,000
Irrigation Segment
Goodwill [Line Items]
Goodwill, Gross			30,177,000	25,136,000
Accumulated impairment losses			0	$ 0
Carrying amount of goodwill
Balance at the beginning of the period		30,177,000	25,136,000
Acquisitions		284,253,000	5,038,000
Impairment			0
Foreign currency translation		(918,000)	3,000
Balance at the end of the period		$ 313,512,000	$ 30,177,000