Fair Value Accounting - Carrying amounts and estimated fair values of long-term debt (Details) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	$ 426.9		$ 878.2
Less: unamortized discount			(8.5)
Less: unamortized debt issuance costs	(2.4)		(2.9)
Recourse, net of unamortized discount and unamortized debt issuance costs	424.2	[1]	866.8
Non-recourse debt	2,882.1		2,401.2
Less: unamortized debt issuance costs	(30.4)		(25.6)
Non-recourse debt, net of unamortized debt issuance costs	2,851.5		2,375.6
Total debt	3,275.7	[1]	3,242.4
2018 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Less: unamortized discount	(0.2)
Carrying Value
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	426.6		869.7
Less: unamortized debt issuance costs	(2.4)		(2.9)
Recourse, net of unamortized discount and unamortized debt issuance costs	424.2		866.8
Non-recourse debt	2,881.9		2,401.2
Less: unamortized debt issuance costs	(30.4)		(25.6)
Non-recourse debt, net of unamortized debt issuance costs	2,851.5		2,375.6
Total debt	3,275.7		3,242.4
Carrying Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	139.4		158.5
Carrying Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	161.7		166.2
Carrying Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	258.9		266.9
Carrying Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	282.3		293.6
Carrying Value | 2018 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	477.3		0.0
Carrying Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	386.7		402.8
Carrying Value | TRIP Master Funding secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	946.9		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	0.0		441.2
Convertible subordinated notes	0.0		449.4
Less: unamortized discount	0.0		(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	26.5		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	0.4		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	228.7		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	415.1		1,144.1
Non-recourse debt	2,883.7		2,459.5
Total debt	3,298.8		3,603.6
Estimated Fair Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	143.2		165.7
Estimated Fair Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	173.6		169.6
Estimated Fair Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	261.3		281.9
Estimated Fair Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	282.3		293.6
Estimated Fair Value | 2018 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	479.9		0.0
Estimated Fair Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	362.2		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	952.5		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	388.2		400.3
Estimated Fair Value | Convertible subordinated notes
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	0.0		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	26.5		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	0.4		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	$ 228.7		$ 150.7

[1] (unaudited)