SEGMENTS - Major Product Categories and Percentage of Consolidated Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Product Information [Line Items]
Net sales	$ 449,422	$ 339,153	$ 841,425	$ 726,227
Sales Revenue, Net | Product Concentration Risk
Product Information [Line Items]
Percentage of consolidated net sales	100.00%	100.00%	100.00%	100.00%
Eliminations
Product Information [Line Items]
Net sales	$ (4,521)	$ (7,884)	$ (11,300)	$ (15,013)
Commercial Trailer Products
Product Information [Line Items]
Net sales	296,103	232,247	542,874	483,192
Commercial Trailer Products | Operating Segments
Product Information [Line Items]
Net sales	296,342	232,254	544,051	483,229
Commercial Trailer Products | Eliminations
Product Information [Line Items]
Net sales	239	7	1,177	37
Diversified Products
Product Information [Line Items]
Net sales	72,296	56,074	140,463	131,933
Diversified Products | Operating Segments
Product Information [Line Items]
Net sales	76,578	63,951	150,586	146,909
Diversified Products | Eliminations
Product Information [Line Items]
Net sales	4,282	7,877	10,123	14,976
Final Mile Products
Product Information [Line Items]
Net sales	81,023	50,832	158,088	111,102
Final Mile Products | Operating Segments
Product Information [Line Items]
Net sales	81,023	50,832	158,088	111,102
Final Mile Products | Eliminations
Product Information [Line Items]
Net sales	0	0	0	0
New trailers
Product Information [Line Items]
Net sales	$ 321,831	$ 246,929	$ 590,762	$ 528,142
New trailers | Sales Revenue, Net | Product Concentration Risk
Product Information [Line Items]
Percentage of consolidated net sales	71.60%	72.80%	70.20%	72.70%
New trailers | Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0	$ 0	$ 0
New trailers | Commercial Trailer Products | Operating Segments
Product Information [Line Items]
Net sales	287,741	218,753	526,406	456,654
New trailers | Diversified Products | Operating Segments
Product Information [Line Items]
Net sales	34,090	28,176	64,356	71,488
New trailers | Final Mile Products | Operating Segments
Product Information [Line Items]
Net sales	0	0	0	0
Used trailers
Product Information [Line Items]
Net sales	$ 378	$ 3,596	$ 1,390	$ 5,124
Used trailers | Sales Revenue, Net | Product Concentration Risk
Product Information [Line Items]
Percentage of consolidated net sales	0.10%	1.10%	0.20%	0.70%
Used trailers | Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0	$ 0	$ 0
Used trailers | Commercial Trailer Products | Operating Segments
Product Information [Line Items]
Net sales	19	2,273	184	2,591
Used trailers | Diversified Products | Operating Segments
Product Information [Line Items]
Net sales	359	1,323	1,206	2,533
Used trailers | Final Mile Products | Operating Segments
Product Information [Line Items]
Net sales	0	0	0	0
Components, parts and service
Product Information [Line Items]
Net sales	$ 32,756	$ 26,306	$ 66,543	$ 58,282
Components, parts and service | Sales Revenue, Net | Product Concentration Risk
Product Information [Line Items]
Percentage of consolidated net sales	7.30%	7.80%	7.90%	8.00%
Components, parts and service | Eliminations
Product Information [Line Items]
Net sales	$ (4,282)	$ (7,884)	$ (10,125)	$ (14,984)
Components, parts and service | Commercial Trailer Products | Operating Segments
Product Information [Line Items]
Net sales	5,529	9,571	11,470	18,843
Components, parts and service | Diversified Products | Operating Segments
Product Information [Line Items]
Net sales	27,544	22,166	57,510	48,248
Components, parts and service | Final Mile Products | Operating Segments
Product Information [Line Items]
Net sales	3,965	2,453	7,688	6,175
Equipment and other
Product Information [Line Items]
Net sales	$ 94,457	$ 62,322	$ 182,730	$ 134,679
Equipment and other | Sales Revenue, Net | Product Concentration Risk
Product Information [Line Items]
Percentage of consolidated net sales	21.00%	18.40%	21.70%	18.50%
Equipment and other | Eliminations
Product Information [Line Items]
Net sales	$ (239)	$ 0	$ (1,175)	$ (29)
Equipment and other | Commercial Trailer Products | Operating Segments
Product Information [Line Items]
Net sales	3,053	1,657	5,991	5,141
Equipment and other | Diversified Products | Operating Segments
Product Information [Line Items]
Net sales	14,585	12,286	27,514	24,640
Equipment and other | Final Mile Products | Operating Segments
Product Information [Line Items]
Net sales	$ 77,058	$ 48,379	$ 150,400	$ 104,927