Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2016		Dec. 31, 2015	Dec. 31, 2006
Derivative [Line Items]
Total stockholders' equity	$ 4,254.4	[1]	$ 4,048.7
AOCL – loss/ (income)
Derivative [Line Items]
Total stockholders' equity	(0.6)		$ (1.3)
Designated as hedging instrument | Interest rate swap, Expired, 2006 secured railcar equipment notes
Derivative [Line Items]
Notional Amount	$ 200.0			$ 200.0
Interest Rate	4.87%
Liability	$ 0.0
Designated as hedging instrument | Interest rate swap, Expired, 2006 secured railcar equipment notes | AOCL – loss/ (income)
Derivative [Line Items]
Total stockholders' equity	(0.8)
Designated as hedging instrument | Interest rate swap, Expired, 2006 secured railcar equipment notes | Noncontrolling Interest
Derivative [Line Items]
Total stockholders' equity	0.0
Designated as hedging instrument | Interest rate swap, Expired, TRIP Holdings warehouse loan
Derivative [Line Items]
Notional Amount	$ 788.5
Interest Rate	3.60%
Liability	$ 0.0
Designated as hedging instrument | Interest rate swap, Expired, TRIP Holdings warehouse loan | AOCL – loss/ (income)
Derivative [Line Items]
Total stockholders' equity	6.4
Designated as hedging instrument | Interest rate swap, Expired, TRIP Holdings warehouse loan | Noncontrolling Interest
Derivative [Line Items]
Total stockholders' equity	8.7
Designated as hedging instrument | Interest rate swap, Open, TRIP Master Funding secured railcar equipment notes
Derivative [Line Items]
Notional Amount	$ 40.3
Interest Rate	2.62%
Liability	$ 1.6
Designated as hedging instrument | Interest rate swap, Open, TRIP Master Funding secured railcar equipment notes | AOCL – loss/ (income)
Derivative [Line Items]
Total stockholders' equity	0.7
Designated as hedging instrument | Interest rate swap, Open, TRIP Master Funding secured railcar equipment notes | Noncontrolling Interest
Derivative [Line Items]
Total stockholders' equity	$ 0.9

[1] (unaudited)