Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
External Revenue	$ 604.8	$ 533.2
Total revenues	604.8	533.2
Operating Profit (Loss)	91.8	62.1
Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	0.0	0.0
Intersegment | Eliminations – Lease subsidiary
Segment Reporting Information [Line Items]
Intersegment Revenues	(270.1)	(296.1)
Total revenues	(270.1)	(296.1)
Operating Profit (Loss)	(27.2)	(28.7)
Intersegment | Eliminations – Other
Segment Reporting Information [Line Items]
Intersegment Revenues	(15.5)	(10.7)
Total revenues	(15.5)	(10.7)
Operating Profit (Loss)	(0.4)	0.1
Total
Segment Reporting Information [Line Items]
Total revenues	604.8	533.2
Rail Group
Segment Reporting Information [Line Items]
External Revenue	333.5	292.0
Rail Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	270.1	296.1
Rail Group | Total
Segment Reporting Information [Line Items]
Total revenues	603.6	588.1
Operating Profit (Loss)	50.6	51.5
Railcar Leasing and Management Services Group
Segment Reporting Information [Line Items]
External Revenue	200.2	174.3
Railcar Leasing and Management Services Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	0.2	0.3
Railcar Leasing and Management Services Group | Total
Segment Reporting Information [Line Items]
Total revenues	200.4	174.6
Operating Profit (Loss)	85.8	71.1
All Other
Segment Reporting Information [Line Items]
External Revenue	71.1	66.9
All Other | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	15.3	10.4
All Other | Total
Segment Reporting Information [Line Items]
Total revenues	86.4	77.3
Operating Profit (Loss)	6.6	5.8
Corporate | Total
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0
Operating Profit (Loss)	$ (23.6)	$ (37.7)