GOODWILL AND INTANGIBLE ASSETS - Carrying Amount of Goodwill by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 24, 2016	Sep. 26, 2015	Sep. 24, 2016	Dec. 26, 2015
Goodwill
Goodwill, Gross				$ 371,808
Carrying amount of goodwill
Balance at the beginning of the period			$ 336,916
Balance at December 26, 2015				(34,892)
Foreign currency translation			(9,053)
Balance at the end of the period	$ 327,863		327,863	336,916
Engineered Support Structures Segment
Goodwill
Goodwill, Gross				101,275
Carrying amount of goodwill
Balance at the beginning of the period			101,275
Foreign currency translation			(4,559)
Balance at the end of the period	96,716		96,716	101,275
Energy and Mining Segment
Goodwill
Goodwill, Gross				99,829
Carrying amount of goodwill
Balance at the beginning of the period			81,159
Balance at December 26, 2015		$ (19)		(18,670)
Foreign currency translation	(4,968)
Balance at the end of the period	76,191		76,191	81,159
Utility Support Structures Segment
Goodwill
Goodwill, Gross				75,404
Carrying amount of goodwill
Balance at the beginning of the period			75,404
Foreign currency translation			0
Balance at the end of the period	75,404		75,404	75,404
Coatings Segment
Goodwill
Goodwill, Gross				75,941
Carrying amount of goodwill
Balance at the beginning of the period			59,719
Balance at December 26, 2015	(9,100)	$ (7)		(16,222)
Foreign currency translation			163
Balance at the end of the period	59,882		59,882	59,719
Irrigation Segment
Goodwill
Goodwill, Gross				19,359
Carrying amount of goodwill
Balance at the beginning of the period			19,359
Foreign currency translation			311
Balance at the end of the period	$ 19,670		$ 19,670	$ 19,359