SEGMENTS - Major Product Categories and Percentage of Consolidated Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Product Information [Line Items]
Net sales	$ 392,003	$ 387,074
Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	100.00%	100.00%
Eliminations
Product Information [Line Items]
Net sales	$ (6,779)	$ (7,129)
Commercial Trailer Products
Product Information [Line Items]
Net sales	246,771	250,945
Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	247,709	250,975
Commercial Trailer Products \| Eliminations
Product Information [Line Items]
Net sales	938	30
Diversified Products
Product Information [Line Items]
Net sales	68,167	75,859
Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	74,008	82,958
Diversified Products \| Eliminations
Product Information [Line Items]
Net sales	5,841	7,099
Final Mile Products
Product Information [Line Items]
Net sales	77,065	60,270
Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	77,065	60,270
Final Mile Products \| Eliminations
Product Information [Line Items]
Net sales	0	0
New trailers
Product Information [Line Items]
Net sales	$ 268,931	$ 281,213
New trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	68.60%	72.70%
New trailers \| Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0
New trailers \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	238,665	237,901
New trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	30,266	43,312
New trailers \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	0	0
Used trailers
Product Information [Line Items]
Net sales	$ 1,012	$ 1,528
Used trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	0.30%	0.40%
Used trailers \| Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0
Used trailers \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	165	318
Used trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	847	1,210
Used trailers \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	0	0
Components, parts and service
Product Information [Line Items]
Net sales	$ 33,787	$ 31,976
Components, parts and service \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	8.60%	8.30%
Components, parts and service \| Eliminations
Product Information [Line Items]
Net sales	$ (5,843)	$ (7,100)
Components, parts and service \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	5,941	9,272
Components, parts and service \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	29,966	26,082
Components, parts and service \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	3,723	3,722
Equipment and other
Product Information [Line Items]
Net sales	$ 88,273	$ 72,357
Equipment and other \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	22.50%	18.70%
Equipment and other \| Eliminations
Product Information [Line Items]
Net sales	$ (936)	$ (29)
Equipment and other \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	2,938	3,484
Equipment and other \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	12,929	12,354
Equipment and other \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	$ 73,342	$ 56,548