Related Party Transactions - Additional Information (Detail) $ in Millions	1 Months Ended	6 Months Ended	18 Months Ended
	Sep. 30, 2015 USD ($) Vehicle	Feb. 28, 2017 USD ($) Vehicle	Feb. 28, 2017 USD ($) Vehicle	Apr. 30, 2010 USD ($) Vehicle
Related Party Transaction [Line Items]
Number of railcars sold | Vehicle		196	3,602
Sale of railcars		$ 2.4	$ 169.6
Number of railcars sold and recognized | Vehicle		3,402	3,402
Revenue recognize from railcars sold			$ 163.0
Deferred revenue on railcars sold			$ 7.8
Deferred revenue, number of railcars sold | Vehicle		389	389
Number of railcars to be sold or disposed | Vehicle		94	94
Number of railcars scrapped | Vehicle		189	189
Proceeds from sale of scrapped railcars		$ 1.2	$ 1.2
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	$ 148.0			$ 256.0
Related party fee	$ 1.0
Profit sharing agreement, amount paid		4.5	4.5
Accrued profit sharing		$ 3.6	$ 3.6