Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands							1 Months Ended		3 Months Ended
ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands	Feb. 11, 2019	Dec. 31, 2018	Oct. 18, 2018	Aug. 03, 2018	Aug. 01, 2018	Jan. 26, 2018	Jan. 31, 2019	Apr. 30, 2016	Mar. 30, 2019	Mar. 31, 2018	Dec. 29, 2018
Business Acquisition [Line Items]
Goodwill									$ 416,996		$ 385,207
United Galvanizing [Member]
Business Acquisition [Line Items]
Cash paid in acquisition	$ 26,000
Property, plant, and equipment acquired	7,216
Consideration transfered	28,000
Contingent consideration liability, current	2,000
Goodwill	$ 15,720
CSP Coatings Systems Of Auckland [Member]
Business Acquisition [Line Items]
Cash paid in acquisition			$ 17,711
Property, plant, and equipment acquired			7,373
Goodwill			$ 5,120
Larson Camouflage [Member]
Business Acquisition [Line Items]
Cash paid in acquisition		$ 31,106
Property, plant, and equipment acquired		1,151
Consideration transfered		$ 34,562
Contingent consideration liability, as percent of purchase price (percent)		10.00%
Goodwill		$ 14,494
Walpar
Business Acquisition [Line Items]
Percentage acquired				72.00%			28.00%
Consideration transfered				$ 57,805			$ 23,082
Goodwill				42,216
Convert Italia S.p.A
Business Acquisition [Line Items]
Business Acquisition, Goodwill, Expected Tax Deductible Amount				$ 0
Percentage acquired				75.00%
Consideration transfered				$ 43,504
Goodwill				$ 34,280
Derit Infrastructure Pvt. Ltd. [Member]
Business Acquisition [Line Items]
Consideration transfered					$ 14,700
Torrent Engineering and Equipment
Business Acquisition [Line Items]
Percentage acquired						60.00%
Consideration transfered						$ 4,800
Goodwill						3,922
Annual revenue of acquiree						9,000
Customer relationships and other intangible assets						$ 4,020
Walpart, Convert, and Torrent [Member]
Business Acquisition [Line Items]
Revenue of acquiree since acquisition									41,557	$ 932
Net earnings of acquiree since acquisition									$ 647	$ 86
IGC Galvanizing Industries (M) Sdn Bhd [Member]
Business Acquisition [Line Items]
Percentage acquired								10.00%
Consideration transfered								$ 5,510
Customer Relationships \| United Galvanizing [Member]
Business Acquisition [Line Items]
Useful life	10 years
Customer relationships and other intangible assets	$ 3,092
Customer Relationships \| CSP Coatings Systems Of Auckland [Member]
Business Acquisition [Line Items]
Useful life			10 years
Customer relationships and other intangible assets			$ 3,113
Customer Relationships \| Larson Camouflage [Member]
Business Acquisition [Line Items]
Useful life		12 years
Customer relationships and other intangible assets		$ 17,050
Customer Relationships \| Walpar
Business Acquisition [Line Items]
Useful life				14 years
Patents & Proprietary Technology \| Convert Italia S.p.A
Business Acquisition [Line Items]
Useful life				15 years
Trade Names \| United Galvanizing [Member]
Business Acquisition [Line Items]
Customer relationships and other intangible assets	$ 894