GOODWILL AND INTANGIBLE ASSETS - Carrying Amount of Goodwill by Segment (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 28, 2019	Dec. 29, 2018
Goodwill
Gross balance, beginning		$ 434,454
Accumulated impairment losses		(49,247)
Balance, ending	$ 421,679	385,207
Carrying amount of goodwill
Balance at the beginning of the period	385,207
Acquisitions	40,647
Foreign currency translation	(4,175)
Balance at the end of the period	421,679
Engineered Support Structures Segment
Goodwill
Gross balance, beginning		204,735
Accumulated impairment losses		(18,670)
Balance, ending	186,065	186,065
Carrying amount of goodwill
Balance at the beginning of the period	186,065
Acquisitions	21,043
Foreign currency translation	(2,652)
Balance at the end of the period	204,456
Utility Support Structures Segment
Goodwill
Gross balance, beginning		123,618
Accumulated impairment losses		(14,355)
Balance, ending	109,263	109,263
Carrying amount of goodwill
Balance at the beginning of the period	109,263
Acquisitions	7,889
Foreign currency translation	(1,758)
Balance at the end of the period	115,394
Coatings Segment
Goodwill
Gross balance, beginning		80,937
Accumulated impairment losses		(16,222)
Balance, ending	64,715	64,715
Carrying amount of goodwill
Balance at the beginning of the period	64,715
Acquisitions	11,715
Foreign currency translation	(133)
Balance at the end of the period	76,297
Irrigation Segment
Goodwill
Gross balance, beginning		25,164
Accumulated impairment losses		0
Balance, ending	25,164	$ 25,164
Carrying amount of goodwill
Balance at the beginning of the period	25,164
Acquisitions	0
Foreign currency translation	368
Balance at the end of the period	$ 25,532