SEGMENTS - Major Product Categories and Percentage of Consolidated Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Product Information [Line Items]
Net sales	$ 580,908	$ 553,073	$ 1,740,135	$ 1,657,082
Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	100.00%	100.00%	100.00%	100.00%
Eliminations
Product Information [Line Items]
Net sales	$ (6,121)	$ (4,679)	$ (21,143)	$ (16,555)
Commercial Trailer Products
Product Information [Line Items]
Net sales	380,062	368,301	1,120,608	1,098,182
Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	380,344	368,342	1,122,253	1,098,271
Commercial Trailer Products \| Eliminations
Product Information [Line Items]
Net sales	282	41	1,645	89
Diversified Products
Product Information [Line Items]
Net sales	87,342	97,723	270,357	275,183
Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	93,181	102,361	289,855	291,649
Diversified Products \| Eliminations
Product Information [Line Items]
Net sales	5,839	4,638	19,498	16,466
Final Mile Products
Product Information [Line Items]
Net sales	113,504	87,049	349,170	283,717
Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	113,504	87,049	349,170	283,717
Final Mile Products \| Eliminations
Product Information [Line Items]
Net sales	0	0	0	0
New trailers
Product Information [Line Items]
Net sales	$ 418,635	$ 398,402	$ 1,225,420	$ 1,165,292
New trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	72.10%	72.00%	70.40%	70.30%
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	366,938	354,003	1,078,599	1,049,452
New trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	51,697	44,399	146,821	115,840
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	$ 503	$ 2,663	$ 1,979	$ 11,283
Used trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	0.10%	0.50%	0.10%	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	86	1,888	236	8,794
Used trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	417	775	1,743	2,489
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	$ 32,171	$ 34,782	$ 111,385	$ 111,549
Components, parts and service \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	5.50%	6.30%	6.40%	6.70%
Components, parts and service \| Eliminations
Product Information [Line Items]
Net sales	$ (5,960)	$ (4,676)	$ (20,455)	$ (16,529)
Components, parts and service \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	10,039	8,090	30,994	25,780
Components, parts and service \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	23,790	29,064	88,681	94,958
Components, parts and service \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	4,302	2,304	12,165	7,340
Equipment and other
Product Information [Line Items]
Net sales	$ 129,599	$ 117,226	$ 401,351	$ 368,958
Equipment and other \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	22.30%	21.20%	23.10%	22.30%
Equipment and other \| Eliminations
Product Information [Line Items]
Net sales	$ (161)	$ (3)	$ (688)	$ (26)
Equipment and other \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	3,281	4,361	12,424	14,245
Equipment and other \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	17,277	28,123	52,610	78,362
Equipment and other \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	$ 109,202	$ 84,745	$ 337,005	$ 276,377