SEGMENTS - Major Product Categories and Percentage of Consolidated Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Product Information [Line Items]
Net sales	$ 626,053	$ 612,690	$ 1,159,227	$ 1,104,009
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	$ (6,654)	$ (5,111)	$ (15,022)	$ (11,876)
Commercial Trailer Products
Product Information [Line Items]
Net sales	400,401	402,484	740,546	729,881
Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	400,864	402,507	741,909	729,929
Commercial Trailer Products \| Eliminations
Product Information [Line Items]
Net sales	463	23	1,363	48
Diversified Products
Product Information [Line Items]
Net sales	90,835	88,997	183,015	177,460
Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	97,026	94,085	196,674	189,288
Diversified Products \| Eliminations
Product Information [Line Items]
Net sales	6,191	5,088	13,659	11,828
Final Mile Products
Product Information [Line Items]
Net sales	134,817	121,209	235,666	196,668
Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	134,817	121,209	235,666	196,668
Final Mile Products \| Eliminations
Product Information [Line Items]
Net sales	0	0	0	0
New trailers
Product Information [Line Items]
Net sales	$ 435,167	$ 422,733	$ 806,785	$ 766,890
New trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	69.50%	69.00%	69.60%	69.50%
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	385,842	385,131	711,661	695,449
New trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	49,325	37,602	95,124	71,441
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	$ 752	$ 3,127	$ 1,476	$ 8,620
Used trailers \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	0.10%	0.50%	0.10%	0.80%
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	13	2,499	150	6,906
Used trailers \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	739	628	1,326	1,714
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	$ 37,501	$ 38,500	$ 79,214	$ 76,767
Components, parts and service \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	6.00%	6.30%	6.80%	7.00%
Components, parts and service \| Eliminations
Product Information [Line Items]
Net sales	$ (6,575)	$ (5,091)	$ (14,495)	$ (11,853)
Components, parts and service \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	10,622	9,042	20,955	17,690
Components, parts and service \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	29,007	31,926	64,891	65,894
Components, parts and service \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	4,447	2,623	7,863	5,036
Equipment and other
Product Information [Line Items]
Net sales	$ 152,633	$ 148,330	$ 271,752	$ 251,732
Equipment and other \| Sales Revenue, Net
Product Information [Line Items]
Percentage of consolidated net sales	24.40%	24.20%	23.40%	7.20%
Equipment and other \| Eliminations
Product Information [Line Items]
Net sales	$ (79)	$ (20)	$ (527)	$ (23)
Equipment and other \| Commercial Trailer Products \| Operating Segments
Product Information [Line Items]
Net sales	4,387	5,835	9,143	9,884
Equipment and other \| Diversified Products \| Operating Segments
Product Information [Line Items]
Net sales	17,955	23,929	35,333	50,239
Equipment and other \| Final Mile Products \| Operating Segments
Product Information [Line Items]
Net sales	$ 130,370	$ 118,586	$ 227,803	$ 191,632