Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Sales
Total Net Sales	$ 543,711	$ 531,350	$ 514,831	$ 437,597	$ 527,477	$ 491,697	$ 486,021	$ 358,120	$ 458,354	$ 439,977	$ 413,126	$ 324,229	$ 2,027,489	$ 1,863,315	$ 1,635,686
Depreciation and amortization													37,998	38,829	38,336
Income (Loss) from operations													180,369	122,386	103,191
Reconciling items to net income
Interest expense													(19,548)	(22,165)	(26,308)
Other, net													2,490	(1,759)	740
Income tax expense													59,022	37,532	31,094
Net income	$ 33,286	$ 31,880	$ 28,649	$ 10,474	$ 19,088	$ 18,307	$ 16,239	$ 7,296	$ 10,423	$ 16,236	$ 14,135	$ 5,735	104,289	60,930	46,529
External Customers
Net Sales
Total Net Sales													2,027,489	1,863,315	1,635,686
Intersegment Sales
Net Sales
Total Net Sales													0	0	0
Commercial Trailer Products
Net Sales
Total Net Sales													1,509,380	1,294,164	1,082,456
Depreciation and amortization													11,574	11,332	11,127
Income (Loss) from operations													158,805	81,141	57,543
Commercial Trailer Products | External Customers
Net Sales
Total Net Sales													1,446,113	1,221,040	1,010,736
Commercial Trailer Products | Intersegment Sales
Net Sales
Total Net Sales													63,267	73,124	71,720
Diversified Products
Net Sales
Total Net Sales													428,021	466,238	458,653
Depreciation and amortization													22,853	23,806	23,320
Income (Loss) from operations													47,940	54,879	59,126
Diversified Products | External Customers
Net Sales
Total Net Sales													415,093	453,160	444,804
Diversified Products | Intersegment Sales
Net Sales
Total Net Sales													12,928	13,078	13,849
Retail
Net Sales
Total Net Sales													167,291	190,080	181,486
Depreciation and amortization													2,136	2,061	2,029
Income (Loss) from operations													4,401	3,785	2,885
Retail | External Customers
Net Sales
Total Net Sales													166,283	189,115	180,146
Retail | Intersegment Sales
Net Sales
Total Net Sales													1,008	965	1,340
Corporate and Eliminations
Net Sales
Total Net Sales													(77,203)	(87,167)	(86,909)
Depreciation and amortization													1,435	1,630	1,860
Income (Loss) from operations													(30,777)	(17,419)	(16,363)
Corporate and Eliminations | External Customers
Net Sales
Total Net Sales													0	0	0
Corporate and Eliminations | Intersegment Sales
Net Sales
Total Net Sales													$ (77,203)	$ (87,167)	$ (86,909)