SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 30, 2017
Disaggregation of Revenue [Line Items]
Contract asset, current	$ 95,209,000	$ 51,507,000
Contract with customer, liability, current	6,301		$ 7,368
Revenue recognized from contract liability	3,000
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	477,285,000
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	221,399,000
Offshore and Other Complex Steel Structures
Disaggregation of Revenue [Line Items]
Contract asset, current			$ 16,165,000
Utility Support Structures Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Utility Support Structures Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	209,859,000
Engineered Support Structures Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	207,194,000
Engineered Support Structures Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,722,000
Coatings Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	68,458,000
Coatings Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Irrigation Segment | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	183,234,000
Irrigation Segment | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,818,000
Other Segments | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	18,399,000
Other Segments | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 0