Derivative Instruments - Effect on statements of operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative Instruments, Gain (Loss) [Line Items]
Expected effect during next twelve months	$ 2.0		$ 2.0
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	0.0	$ 0.0	(0.1)	$ (0.1)
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	0.5	1.1	1.2	2.3
Expected effect during next twelve months	2.0		2.0
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	0.0	$ 0.1	0.1	$ 0.3
Expected effect during next twelve months	$ 0.2		$ 0.2