Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	May. 31, 2015 USD ($) Segment	May. 31, 2014 USD ($)	Aug. 31, 2014 USD ($)	Jul. 18, 2014
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			3
Total revenue	$ 714,606	$ 593,285	$ 1,839,813	$ 1,585,856
Total assets	1,727,115		1,727,115		$ 1,517,168
Earnings (loss) from unconsolidated affiliates	982	$ 298	1,552	$ 272
Investment in unconsolidated affiliates	91,217		91,217		69,359
GBW Railcar Services Holdings, LLC
Segment Reporting Information [Line Items]
Equity method investment, percentage of ownership interest						50.00%
Total revenue	88,800		254,700
Total assets	230,100		230,100		$ 210,600
Earnings (loss) from unconsolidated affiliates	400		400
Investment in unconsolidated affiliates	$ 57,600		$ 57,600
GBW Railcar Services Holdings, LLC | Watco Companies LLC
Segment Reporting Information [Line Items]
Equity method investment, percentage of ownership interest						50.00%