GOODWILL AND INTANGIBLE ASSETS (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Goodwill [Line Items]
Goodwill, Gross		$ 321,110
Carrying amount of goodwill
Balance at the beginning of the period	$ 321,110	371,808
Acquisitions		(34,892)
Acquisition		336,916
Foreign currency translation	13,161	(15,806)
Balance at the end of the period	337,720	321,110	$ 371,808
Engineered Support Structures
Goodwill [Line Items]
Goodwill, Gross		139,019
Carrying amount of goodwill
Balance at the beginning of the period	139,019	170,341
Acquisitions		(18,670)
Acquisition		151,671
Foreign currency translation		(12,652)
Balance at the end of the period	151,406	139,019	170,341
Utility Support Structures Segment
Goodwill [Line Items]
Goodwill, Gross		88,451
Carrying amount of goodwill
Balance at the beginning of the period	88,451	88,680
Acquisitions		0	(19,000)
Acquisition		88,680
Foreign currency translation		(229)
Balance at the end of the period	90,248	88,451	88,680
Coatings Segment
Goodwill [Line Items]
Goodwill, Gross		59,569
Carrying amount of goodwill
Balance at the beginning of the period	59,569	75,941
Acquisitions		(16,222)
Acquisition		59,719
Foreign currency translation		(150)
Balance at the end of the period	60,474	59,569	75,941
Irrigation Segment
Goodwill [Line Items]
Goodwill, Gross		19,611
Carrying amount of goodwill
Balance at the beginning of the period	19,611	19,359
Acquisitions		0	(16,222)
Acquisition		19,359
Foreign currency translation		252
Balance at the end of the period	19,778	19,611	19,359
Other
Goodwill [Line Items]
Goodwill, Gross		14,460
Carrying amount of goodwill
Balance at the beginning of the period	14,460	17,487
Acquisitions		0
Acquisition		17,487
Foreign currency translation		(3,027)
Balance at the end of the period	$ 15,814	$ 14,460	$ 17,487