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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018	Dec. 29, 2018
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 692,139	$ 698,684
Contract with customer, liability, current	6,420		$ 4,906
Revenue recognized from contract liability	1,030	2,824
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	467,361	477,285
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	224,778	221,399
Utility Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	243,258	209,859
Utility Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	30,292	0
Utility Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	212,966	209,859
Engineered Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	227,969	215,916
Engineered Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	218,980	207,194
Engineered Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,989	8,722
Coatings Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	70,231	68,458
Coatings Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	70,231	68,458
Coatings Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Irrigation Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	150,681	186,052
Irrigation Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	147,858	183,234
Irrigation Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,823	2,818
Other Segments \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	18,399
Other Segments \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 0	$ 0