GOODWILL IMPAIRMENT - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 204,351	$ 204,418	$ 204,420	$ 311,026	$ 311,084
Goodwill impairment loss	0	0	106,737
Tank Trailers Reporting Unit
Goodwill [Line Items]
Goodwill impairment loss			11,000
Final Mile Product Reporting Unit
Goodwill [Line Items]
Goodwill impairment loss			95,800
Commercial Trailer Products
Goodwill [Line Items]
Goodwill	2,625	2,625	2,625	2,625	2,625
Goodwill impairment loss	0	0	0
Commercial Trailer Products | Tank Trailers Reporting Unit
Goodwill [Line Items]
Goodwill				98,400
Commercial Trailer Products | Process Systems Reporting Unit
Goodwill [Line Items]
Goodwill				42,300
Diversified Products
Goodwill [Line Items]
Goodwill	129,777	129,844	129,846	140,686	140,744
Goodwill impairment loss	0	0	10,971
Final Mile Products
Goodwill [Line Items]
Goodwill	71,949	71,949	71,949	$ 167,715	$ 167,715
Goodwill impairment loss	$ 0	$ 0	$ 95,766