Segment Information - Segments Internal Financial Reports (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018	Aug. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 658,671	$ 629,336	$ 1,263,194	$ 1,188,871
Earnings (loss) from operations	18,054	60,870	54,508	122,312
Assets	2,533,221		2,533,221		$ 2,465,464
Manufacturing
Segment Reporting Information [Line Items]
Revenues	476,019	511,827	947,808	963,312
Earnings (loss) from operations	13,990	63,185	50,845	116,154
Wheels, Repair & Parts
Segment Reporting Information [Line Items]
Revenues	125,278	88,710	233,821	166,721
Earnings (loss) from operations	2,823	5,119	6,070	7,537
Leasing & Services
Segment Reporting Information [Line Items]
Revenues	57,374	28,799	81,565	58,838
Earnings (loss) from operations	21,030	16,114	38,543	44,304
Operating Segments | Manufacturing
Segment Reporting Information [Line Items]
Revenues	522,874	525,775	1,000,864	994,064
Earnings (loss) from operations	16,348	66,600	53,636	123,755
Assets	1,093,593		1,093,593		1,020,757
Operating Segments | Wheels, Repair & Parts
Segment Reporting Information [Line Items]
Revenues	134,136	97,661	258,660	183,404
Earnings (loss) from operations	1,965	5,899	5,524	9,065
Assets	341,317		341,317		306,756
Operating Segments | Leasing & Services
Segment Reporting Information [Line Items]
Revenues	60,285	33,164	90,475	64,808
Earnings (loss) from operations	23,131	19,908	46,096	49,470
Assets	704,016		704,016		578,818
Operating Segments | Unallocated Amount to Segment
Segment Reporting Information [Line Items]
Assets	394,295		394,295		$ 559,133
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(58,624)	(27,264)	(86,805)	(53,405)
Earnings (loss) from operations	(3,601)	(7,989)	(9,798)	(14,295)
Intersegment Eliminations | Manufacturing
Segment Reporting Information [Line Items]
Revenues	46,855	13,948	53,056	30,752
Earnings (loss) from operations	2,358	3,415	2,791	7,601
Intersegment Eliminations | Wheels, Repair & Parts
Segment Reporting Information [Line Items]
Revenues	8,858	8,951	24,839	16,683
Earnings (loss) from operations	(858)	780	(546)	1,528
Intersegment Eliminations | Leasing & Services
Segment Reporting Information [Line Items]
Revenues	2,911	4,365	8,910	5,970
Earnings (loss) from operations	2,101	3,794	7,553	5,166
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenues	0		0
Earnings (loss) from operations	$ (19,789)	$ (23,548)	$ (40,950)	$ (45,683)