Related Party Transactions - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Vehicle	May 31, 2016 USD ($) Vehicle	May 31, 2015 USD ($)	May 31, 2016 USD ($) Vehicle	May 31, 2015 USD ($)	Apr. 30, 2010 USD ($) Vehicle
Related Party Transaction [Line Items]
Number of railcars sold and recognized | Vehicle		2,766		2,766
Revenue		$ 612,866	$ 714,606	$ 2,084,334	$ 1,839,813
Sale of railcars				$ 162,000
Number of railcars sold | Vehicle		3,159		3,159
Deferred revenue on railcars sold				$ 7,800
Deferred revenue, number of railcars sold | Vehicle		389		389
Percentage of rate of return the company is entitled to receive after recoup of total investment				25.00%
Percentage of profit sharing after defined levels have been met				100.00%
WL Ross & Co., LLC (WL Ross)
Related Party Transaction [Line Items]
Number of related party railcars purchased | Vehicle	3,885					4,000
Value of railcars	$ 148,000					$ 256,000
Related party fee	$ 1,000
Revenue				$ 154,200
Profit sharing agreement, amount paid		$ 7,200		7,200
Accrued profit sharing		$ 11,300		$ 11,300