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GOODWILL AND OTHER INTANGIBLE ASSETS - Narrative (Details) - USD ($)		3 Months Ended			12 Months Ended
	Oct. 01, 2020	Dec. 31, 2020	Mar. 31, 2020	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill		$ 199,560,000			$ 199,560,000	$ 311,026,000	$ 311,084,000
Goodwill, gross		307,960,000			307,960,000	312,689,000	317,691,000
Goodwill, impairment loss	$ 0			$ 4,900,000	106,737,000
Amortization of intangibles					21,981,000	20,471,000	19,468,000
2021		23,000,000.0			23,000,000.0
2022		17,900,000			17,900,000
2023		15,300,000			15,300,000
2024		15,100,000			15,100,000
2025		14,000,000.0			14,000,000.0
Beall Tank Trailers \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Goodwill [Line Items]
Impairment of intangible assets		1,100,000
Tank Trailers Reporting Unit
Goodwill [Line Items]
Goodwill, impairment loss			$ 11,000,000.0
Commercial Trailer Products
Goodwill [Line Items]
Goodwill		2,625,000			2,625,000	2,625,000	2,625,000
Goodwill, gross		4,288,000			4,288,000	4,288,000	4,288,000
Goodwill, impairment loss					0
Diversified Products
Goodwill [Line Items]
Goodwill		124,986,000			124,986,000	140,686,000	140,744,000
Goodwill, gross		135,957,000			135,957,000	140,686,000	145,688,000
Goodwill, impairment loss				$ 4,900,000	10,971,000
Diversified Products \| Tank Trailers Reporting Unit
Goodwill [Line Items]
Goodwill						98,400,000
Diversified Products \| Process Systems Reporting Unit
Goodwill [Line Items]
Goodwill						42,300,000
Final Mile Products
Goodwill [Line Items]
Goodwill		71,949,000			71,949,000	167,715,000	167,715,000
Goodwill, gross		$ 167,715,000			167,715,000	$ 167,715,000	$ 167,715,000
Goodwill, impairment loss			$ 95,800,000		$ 95,766,000