GOODWILL AND INTANGIBLE ASSETS - Carrying Amount of Goodwill by Segment (Details) $ in Thousands	6 Months Ended
	Jul. 01, 2017 USD ($)
Carrying amount of goodwill
Balance at the beginning of the period	$ 321,110
Foreign currency translation	8,598
Balance at the end of the period	329,708
Engineered Support Structures Segment
Carrying amount of goodwill
Balance at the beginning of the period	94,314
Foreign currency translation	2,885
Balance at the end of the period	97,199
Energy and Mining Segment
Carrying amount of goodwill
Balance at the beginning of the period	72,212
Foreign currency translation	4,628
Balance at the end of the period	76,840
Utility Support Structures Segment
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
Coatings Segment
Carrying amount of goodwill
Balance at the beginning of the period	59,569
Foreign currency translation	483
Balance at the end of the period	60,052
Irrigation Segment
Carrying amount of goodwill
Balance at the beginning of the period	19,611
Foreign currency translation	602
Balance at the end of the period	$ 20,213