SEGMENTS Major Product Categories and Percentage of Consolidated Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Product Information [Line Items]
Net sales	$ 533,174	$ 491,319
Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	100.00%	100.00%
Eliminations
Product Information [Line Items]
Net sales	$ (8,368)	$ (6,765)
Commercial Trailer Products
Product Information [Line Items]
Net sales	340,145	327,397
Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	341,045	327,422
Commercial Trailer Products \| Eliminations
Product Information [Line Items]
Net sales	(900)	(25)
Diversified Products
Product Information [Line Items]
Net sales	92,180	88,463
Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	99,648	95,203
Diversified Products \| Eliminations
Product Information [Line Items]
Net sales	(7,468)	(6,740)
Final Mile Products
Product Information [Line Items]
Net sales	100,849	75,459
Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	100,849	75,459
Final Mile Products \| Eliminations
Product Information [Line Items]
Net sales	0	0
New trailers
Product Information [Line Items]
Net sales	$ 371,618	$ 344,157
New trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	69.70%	70.00%
New trailers \| Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0
New trailers \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	325,819	310,318
New trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	45,799	33,839
New trailers \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	0	0
Used trailers
Product Information [Line Items]
Net sales	$ 724	$ 5,493
Used trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	0.10%	1.10%
Used trailers \| Eliminations
Product Information [Line Items]
Net sales	$ 0	$ 0
Used trailers \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	137	4,407
Used trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	587	1,086
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	$ 41,713	$ 38,267
Components, parts and service \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	7.80%	7.80%
Components, parts and service \| Eliminations
Product Information [Line Items]
Net sales	$ (7,920)	$ (6,762)
Components, parts and service \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	10,333	8,648
Components, parts and service \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	35,884	33,968
Components, parts and service \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	3,416	2,413
Equipment and other
Product Information [Line Items]
Net sales	$ 119,119	$ 103,402
Equipment and other \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	22.30%	21.00%
Equipment and other \| Eliminations
Product Information [Line Items]
Net sales	$ (448)	$ (3)
Equipment and other \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	4,756	4,049
Equipment and other \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	17,378	26,310
Equipment and other \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	$ 97,433	$ 73,046