Fair Value Accounting - Carrying amounts and estimated fair values of long-term debt (Details) - USD ($) $ in Millions	Mar. 31, 2018		Dec. 31, 2017
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	$ 877.3		$ 878.2
Less: unamortized discount	(3.6)	[1]	(8.5)
Less: unamortized debt issuance costs	(2.7)		(2.9)
Recourse, net of unamortized discount and unamortized debt issuance costs	871.0	[1]	866.8
Non-recourse debt	2,380.3		2,401.2
Less: unamortized debt issuance costs	(27.9)		(25.6)
Non-recourse debt, net of unamortized debt issuance costs	2,352.4		2,375.6
Total debt	3,223.4	[1]	3,242.4
Carrying Value
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	873.7		869.7
Less: unamortized debt issuance costs	(2.7)		(2.9)
Recourse, net of unamortized discount and unamortized debt issuance costs	871.0		866.8
Non-recourse debt	2,380.3		2,401.2
Less: unamortized debt issuance costs	(27.9)		(25.6)
Non-recourse debt, net of unamortized debt issuance costs	2,352.4		2,375.6
Total debt	3,223.4		3,242.4
Carrying Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	152.8		158.5
Carrying Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	164.8		166.2
Carrying Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	264.3		266.9
Carrying Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	289.8		293.6
Carrying Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	397.1		402.8
Carrying Value | TRIP Master Funding secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	957.0		962.5
Carrying Value | Senior notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	399.7		399.7
Carrying Value | Convertible subordinated notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	446.1		441.2
Convertible subordinated notes	449.4		449.4
Less: unamortized discount	(3.3)		(8.2)
Carrying Value | Capital lease obligations
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	27.4		28.3
Carrying Value | Other
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	0.5		0.5
Carrying Value | Line of credit | TILC warehouse facility | Revolving credit facility
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	154.5		150.7
Estimated Fair Value
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	1,039.7		1,144.1
Non-recourse debt	2,411.8		2,459.5
Total debt	3,451.5		3,603.6
Estimated Fair Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	161.6		165.7
Estimated Fair Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	181.2		169.6
Estimated Fair Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	272.3		281.9
Estimated Fair Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	289.8		293.6
Estimated Fair Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	376.8		390.4
Estimated Fair Value | TRIP Master Funding secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	975.6		1,007.6
Estimated Fair Value | Senior notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	399.3		400.3
Estimated Fair Value | Convertible subordinated notes
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	612.5		715.0
Estimated Fair Value | Capital lease obligations
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	27.4		28.3
Estimated Fair Value | Other
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	0.5		0.5
Estimated Fair Value | Line of credit | TILC warehouse facility | Revolving credit facility
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	$ 154.5		$ 150.7

[1] (unaudited)