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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 678,692,000	$ 680,779,000	$ 2,059,781,000	$ 2,030,989,000
Contract asset, current	112,620,000		112,620,000		$ 67,672,000	$ 16,165,000
Contract with customer, liability, current	5,088		5,088			7,368
Revenue recognized from contract liability			4,456,000
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	451,295,000		1,403,321,000
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	227,397,000		656,460,000
Offshore and Other Complex Steel Structures
Disaggregation of Revenue [Line Items]
Contract asset, current						$ 16,165,000
Utility Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	217,943,000	203,574,000	624,333,000	613,226,000
Utility Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	6,090,000		6,090,000
Utility Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	211,853,000		618,243,000
Engineered Support Structures Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	248,431,000	244,675,000	710,388,000	669,029,000
Engineered Support Structures Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	235,948,000		680,863,000
Engineered Support Structures Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,483,000		29,525,000
Coatings Segment
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	74,547,000	67,680,000	217,544,000	191,612,000
Coatings Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	74,547,000		217,544,000
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	137,771,000	$ 145,050,000	484,436,000	$ 496,656,000
Irrigation Segment \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	134,710,000		475,744,000
Irrigation Segment \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,061,000		8,692,000
Other Segments \| Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		23,080,000
Other Segments \| Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		0
Difference between Revenue Guidance in Effect before and after Topic 606 \| Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,597,000		34,860,000
Contract asset, current	$ 86,251,000		$ 86,251,000		$ 51,507,000