Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Net Sales
Total Net Sales	$ 471,438	$ 514,831	$ 919,114	$ 952,428
Income (Loss) from operations	58,872	42,054	107,056	69,317
Assets	986,593	994,802	986,593	994,802	$ 949,670
External Customers
Net Sales
Total Net Sales	471,438	514,831	919,114	952,428
Intersegment Sales
Net Sales
Total Net Sales	0	0	0	0
Commercial Trailer Products
Net Sales
Total Net Sales	382,212	412,664	746,252	741,853
Income (Loss) from operations	57,135	39,249	107,392	62,159
Assets	353,270	381,821	353,270	381,821
Commercial Trailer Products | External Customers
Net Sales
Total Net Sales	382,207	412,641	746,237	741,657
Commercial Trailer Products | Intersegment Sales
Net Sales
Total Net Sales	5	23	15	196
Diversified Products
Net Sales
Total Net Sales	92,870	105,306	179,159	216,446
Income (Loss) from operations	10,258	9,769	17,247	21,124
Assets	394,233	424,518	394,233	424,518
Diversified Products | External Customers
Net Sales
Total Net Sales	89,231	102,190	172,877	210,771
Diversified Products | Intersegment Sales
Net Sales
Total Net Sales	3,639	3,116	6,282	5,675
Corporate and Eliminations
Net Sales
Total Net Sales	(3,644)	(3,139)	(6,297)	(5,871)
Income (Loss) from operations	(8,521)	(6,964)	(17,583)	(13,966)
Assets	239,090	188,463	239,090	188,463
Corporate and Eliminations | External Customers
Net Sales
Total Net Sales	0	0	0	0
Corporate and Eliminations | Intersegment Sales
Net Sales
Total Net Sales	$ (3,644)	$ (3,139)	$ (6,297)	$ (5,871)