Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Sales
Total Net Sales	$ 462,057	$ 464,272	$ 471,439	$ 447,676	$ 543,711	$ 531,350	$ 514,831	$ 437,597	$ 527,477	$ 491,697	$ 486,021	$ 358,120	$ 1,845,444	$ 2,027,489	$ 1,863,315
Depreciation and amortization													36,769	37,998	38,829
Income (Loss) from operations													202,532	180,369	122,386
Assets	898,733				949,670				927,446				898,733	949,670	927,446
Reconciling items to net income
Interest expense													(15,663)	(19,548)	(22,165)
Other, net													(1,452)	2,490	(1,759)
Income tax expense													65,984	59,022	37,532
Net income	23,000	$ 33,378	$ 35,532	$ 27,523	33,286	$ 31,880	$ 28,649	$ 10,474	19,088	$ 18,307	$ 16,239	$ 7,296	119,433	104,289	60,930
External Customers
Net Sales
Total Net Sales													1,845,444	2,027,489	1,863,315
Intersegment Sales
Net Sales
Total Net Sales													0	0	0
Commercial Trailer Products
Net Sales
Total Net Sales													1,506,110	1,582,241	1,380,623
Depreciation and amortization													12,345	12,674	12,331
Income (Loss) from operations													212,351	159,385	82,290
Assets	312,848				336,235				342,015				312,848	336,235	342,015
Commercial Trailer Products | External Customers
Net Sales
Total Net Sales													1,506,070	1,582,019	1,380,195
Commercial Trailer Products | Intersegment Sales
Net Sales
Total Net Sales													40	222	428
Diversified Products
Net Sales
Total Net Sales													352,404	456,927	494,992
Depreciation and amortization													22,970	23,888	24,868
Income (Loss) from operations													24,595	51,078	57,635
Assets	370,338				397,892				422,322				370,338	397,892	422,322
Diversified Products | External Customers
Net Sales
Total Net Sales													339,374	445,470	483,120
Diversified Products | Intersegment Sales
Net Sales
Total Net Sales													13,030	11,457	11,872
Corporate and Eliminations
Net Sales
Total Net Sales													(13,070)	(11,679)	(12,300)
Depreciation and amortization													1,454	1,436	1,630
Income (Loss) from operations													(34,414)	(30,094)	(17,539)
Assets	$ 215,547				$ 215,543				$ 163,109				215,547	215,543	163,109
Corporate and Eliminations | External Customers
Net Sales
Total Net Sales													0	0	0
Corporate and Eliminations | Intersegment Sales
Net Sales
Total Net Sales													$ (13,070)	$ (11,679)	$ (12,300)