Segments Internal Financial Reports (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014	Aug. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 630,149	$ 502,216	$ 1,125,207	$ 992,571
Earnings (loss) from operations	92,532	34,602	146,954	72,824
Assets	1,690,409		1,690,409		1,517,168
Manufacturing
Segment Reporting Information [Line Items]
Revenues	505,241	347,755	885,190	707,228
Wheels & Parts
Segment Reporting Information [Line Items]
Revenues	102,640	136,540	189,264	249,941
Leasing & Services
Segment Reporting Information [Line Items]
Revenues	22,268	17,921	50,753	35,402
External Customers
Segment Reporting Information [Line Items]
Revenues	630,149	502,216	1,125,207	992,571
Earnings (loss) from operations	92,532	34,602	146,954	72,824
Operating Segments | Manufacturing
Segment Reporting Information [Line Items]
Revenues	505,322	347,755	892,691	707,228
Earnings (loss) from operations	90,885	30,112	143,722	68,426
Assets	663,567		663,567		521,711
Operating Segments | Wheels & Parts
Segment Reporting Information [Line Items]
Revenues	108,574	138,847	202,109	253,901
Earnings (loss) from operations	8,629	3,616	17,345	3,274
Assets	291,358		291,358		298,009
Operating Segments | Leasing & Services
Segment Reporting Information [Line Items]
Revenues	40,895	23,335	82,564	43,691
Earnings (loss) from operations	28,438	15,056	52,664	26,594
Assets	516,835		516,835		436,075
Operating Segments | Unallocated Amount to Segment
Segment Reporting Information [Line Items]
Assets	218,649		218,649		261,373
Operating Segments | External Customers | Manufacturing
Segment Reporting Information [Line Items]
Revenues	505,241	347,755	885,190	707,228
Earnings (loss) from operations	90,876	30,112	142,927	68,426
Operating Segments | External Customers | Wheels & Parts
Segment Reporting Information [Line Items]
Revenues	102,640	136,540	189,264	249,941
Earnings (loss) from operations	7,976	3,574	15,908	3,201
Operating Segments | External Customers | Leasing & Services
Segment Reporting Information [Line Items]
Revenues	22,268	17,921	50,753	35,402
Earnings (loss) from operations	9,811	9,636	20,853	18,305
Operating Segments | Inter Segment | Manufacturing
Segment Reporting Information [Line Items]
Revenues	81		7,501
Earnings (loss) from operations	9		795
Operating Segments | Inter Segment | Wheels & Parts
Segment Reporting Information [Line Items]
Revenues	5,934	2,307	12,845	3,960
Earnings (loss) from operations	653	42	1,437	73
Operating Segments | Inter Segment | Leasing & Services
Segment Reporting Information [Line Items]
Revenues	18,627	5,414	31,811	8,289
Earnings (loss) from operations	18,627	5,420	31,811	8,289
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(24,642)	(7,721)	(52,157)	(12,249)
Earnings (loss) from operations	(19,289)	(5,462)	(34,043)	(8,362)
Intersegment Eliminations | Inter Segment
Segment Reporting Information [Line Items]
Revenues	(24,642)	(7,721)	(52,157)	(12,249)
Earnings (loss) from operations	(19,289)	(5,462)	(34,043)	(8,362)
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Earnings (loss) from operations	(16,131)	(8,720)	(32,734)	(17,108)
Corporate, Non-Segment | External Customers
Segment Reporting Information [Line Items]
Earnings (loss) from operations	$ (16,131)	$ (8,720)	$ (32,734)	$ (17,108)