Derivative Instruments - Effect on statements of operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative Instruments, Gain (Loss) [Line Items]
Expected effect during next twelve months	$ 2.8		$ 2.8
Interest expense | Designated as hedging instrument | Interest rate swap, Expired, 2006 secured railcar equipment notes
Derivative Instruments, Gain (Loss) [Line Items]
Effect on interest expense	(0.1)	$ (0.1)	(0.2)	$ (0.3)
Expected effect during next twelve months	(0.1)		(0.1)
Interest expense | Designated as hedging instrument | Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative Instruments, Gain (Loss) [Line Items]
Effect on interest expense	1.1	1.2	3.4	3.6
Expected effect during next twelve months	2.8		2.8
Interest expense | Designated as hedging instrument | Interest rate swap, Open, TRIP Master Funding secured railcar equipment notes
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivative, net	0.1	$ 0.2	0.4	$ 0.7
Expected effect during next twelve months	$ 0.3		$ 0.3