Results of Operations for GBW Joint Venture (Detail) - USD ($) $ in Thousands		3 Months Ended
		Nov. 30, 2016	Nov. 30, 2015	Aug. 31, 2016
Segment Reporting Information [Line Items]
Revenue		$ 552,314	$ 802,389
Earnings (loss) from operations		72,660	148,485
Assets		1,817,350		$ 1,835,774
GBW Railcar Services LLC
Segment Reporting Information [Line Items]
Revenue		70,253	95,982
Earnings (loss) from operations		(4,561)	$ 2,408
Assets	[1]	$ 238,303		$ 247,610

[1] Includes goodwill and intangible assets of $92.5 million and $93.4 million as of November 30, 2016 and August 31, 2016.