Derivative Instruments - Effect on statements of operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative [Line Items]
Expected effect during next twelve months	$ 2.2
Interest expense | Designated as hedging instrument | Interest rate swap, Expired, 2006 secured railcar equipment notes
Derivative [Line Items]
Expired hedges	(0.3)	$ (0.4)	$ (0.3)
Expected effect during next twelve months	(0.1)
Interest expense | Designated as hedging instrument | Interest rate swap, Expired, Promissory notes
Derivative [Line Items]
Expired hedges	0.0	0.0	6.5
Expected effect during next twelve months	0.0
Interest expense | Designated as hedging instrument | Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative [Line Items]
Expired hedges	4.5	4.8	4.9
Expected effect during next twelve months	2.2
Interest expense | Designated as hedging instrument | Interest Rate Swap, Open, TRIP Master Funding secured railcar equipment notes
Derivative [Line Items]
Open hedges	0.4	$ 0.9	$ 1.3
Expected effect during next twelve months	$ 0.2