Open-Top Hoppers - Additional Information (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2014 Railcar
Long Lived Assets Held-for-sale [Line Items]
Number of cars held for disposal | Railcar		126
Rail Cars [Member]
Long Lived Assets Held-for-sale [Line Items]
Anticipated proceeds from disposal of cars	$ 952
Gain on disposal of cars	$ 538