Financial Data of Business Segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Segment Vessel	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2015
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment									$ 18.0	$ 10.8	$ 12.0
Number of business segments | Segment									4
Profitability
Lease revenue									$ 1,092.7	1,087.8	1,098.1
Marine operating revenue									195.7	196.0	193.4
Other revenue									105.4	77.1	85.4
Total Revenues	$ 356.7	$ 360.7	$ 359.4	$ 317.0	$ 356.4	$ 349.7	$ 349.5	$ 305.3	1,393.8	1,360.9	1,376.9
Maintenance expense									338.9	321.8	328.3
Marine operating expense									133.2	130.9	131.0
Depreciation									331.9	321.9	307.3
Operating lease expense									54.4	49.6	62.5
Other operating expense									31.3	33.1	34.4
Total Expenses									889.7	857.3	863.5
Net gain on asset dispositions									62.1	72.8	54.1
Interest expense, net									(186.6)	(168.6)	(160.5)
Other (expense) income									(7.9)	(21.6)	(12.6)
Share of affiliates' earnings (pre-tax)									94.5	61.1	55.9
Segment profit (loss)									466.2	447.3	450.3
SG&A									188.6	191.1	180.0
Income tax benefit									48.4	34.1	(243.7)
Net Income	56.6	$ 45.1	$ 68.0	$ 41.5	49.2	$ 47.0	$ 38.8	$ 76.3	211.2	211.3	502.0
Disposition Gains on Owned Assets									58.6	64.8	44.1
Nonoperating Income, Residual Sharing Income									1.9	2.5	10.2
Nonremarketing Disposition Gain (Loss)									8.2	14.5	8.4
Asset Impairment Charges									(6.6)	(9.0)	(8.6)
Selected Balance Sheet Data
Investments in affiliated companies	512.6				464.5				512.6	464.5	441.0
Identifiable assets	8,285.1				7,616.7				8,285.1	7,616.7	7,422.4
Capital Expenditures
Portfolio investments and capital additions									$ (741.7)	(943.4)	(603.4)
ASC [Member]
Segment Reporting Information [Line Items]
Number Of Vessels | Vessel									9
Profitability
Lease revenue									$ 4.2	4.1	4.1
Marine operating revenue									187.5	181.7	168.4
Other revenue									0.0	0.0	0.0
Total Revenues									191.7	185.8	172.5
Maintenance expense									24.5	22.6	22.2
Marine operating expense									114.3	114.1	106.2
Depreciation									10.6	10.6	12.0
Operating lease expense									0.0	0.0	1.8
Other operating expense									0.0	0.0	0.0
Total Expenses									149.4	147.3	142.2
Net gain on asset dispositions									10.5	0.1	(1.9)
Interest expense, net									(6.1)	(5.7)	(5.2)
Other (expense) income									(0.6)	0.1	1.3
Share of affiliates' earnings (pre-tax)									0.0	0.0	0.0
Segment profit (loss)									46.1	33.0	24.5
Disposition Gains on Owned Assets									0.0	0.1	(1.8)
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									10.5	0.0	(0.1)
Asset Impairment Charges									0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0				0.0				0.0	0.0	0.0
Identifiable assets	291.1				297.8				291.1	297.8	286.7
Capital Expenditures
Portfolio investments and capital additions									(18.9)	(15.8)	(14.0)
Rail North America [Member]
Profitability
Lease revenue									868.3	873.4	899.9
Marine operating revenue									0.0	0.0	0.0
Other revenue									96.2	68.1	77.5
Total Revenues									964.5	941.5	977.4
Maintenance expense									267.9	254.7	265.0
Marine operating expense									0.0	0.0	0.0
Depreciation									256.9	248.5	239.4
Operating lease expense									54.4	49.6	60.7
Other operating expense									23.9	27.3	28.7
Total Expenses									603.1	580.1	593.8
Net gain on asset dispositions									54.6	76.3	45.2
Interest expense, net									(134.5)	(125.2)	(121.2)
Other (expense) income									(5.3)	(5.2)	(5.9)
Share of affiliates' earnings (pre-tax)									0.0	0.6	(2.4)
Segment profit (loss)									276.2	307.9	299.3
Disposition Gains on Owned Assets									58.5	64.7	44.0
Nonoperating Income, Residual Sharing Income									0.4	1.4	0.6
Nonremarketing Disposition Gain (Loss)									(3.9)	10.8	5.2
Asset Impairment Charges									(0.4)	(0.6)	(4.6)
Selected Balance Sheet Data
Investments in affiliated companies					0.2					0.2	6.8
Identifiable assets	5,646.7				5,236.6				5,646.7	5,236.6	4,915.0
Capital Expenditures
Portfolio investments and capital additions									(502.2)	(737.4)	(460.9)
Rail International [Member]
Profitability
Lease revenue									219.2	209.3	190.3
Marine operating revenue									0.0	0.0	0.0
Other revenue									8.5	8.2	6.8
Total Revenues									227.7	217.5	197.1
Maintenance expense									46.5	44.5	41.1
Marine operating expense									0.0	0.0	0.0
Depreciation									57.8	55.5	48.9
Operating lease expense									0.0	0.0	0.0
Other operating expense									6.8	5.8	4.7
Total Expenses									111.1	105.8	94.7
Net gain on asset dispositions									1.7	(0.2)	3.1
Interest expense, net									(40.6)	(35.9)	(33.4)
Other (expense) income									1.2	(7.0)	(3.2)
Share of affiliates' earnings (pre-tax)									0.0	0.0	(0.1)
Segment profit (loss)									78.9	68.6	68.8
Disposition Gains on Owned Assets									0.1	0.0	0.1
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									1.6	3.7	3.3
Asset Impairment Charges									0.0	(3.9)	(0.3)
Selected Balance Sheet Data
Investments in affiliated companies	0.0				0.0				0.0	0.0	0.0
Identifiable assets	1,486.7				1,363.2				1,486.7	1,363.2	1,332.9
Capital Expenditures
Portfolio investments and capital additions									(215.7)	(152.7)	(90.9)
Portfolio Management [Member]
Profitability
Lease revenue									1.0	1.0	3.8
Marine operating revenue									8.2	14.3	25.0
Other revenue									0.7	0.8	1.1
Total Revenues									9.9	16.1	29.9
Maintenance expense									0.0	0.0	0.0
Marine operating expense									18.9	16.8	24.8
Depreciation									6.6	7.3	7.0
Operating lease expense									0.0	0.0	0.0
Other operating expense									0.6	0.0	1.0
Total Expenses									26.1	24.1	32.8
Net gain on asset dispositions									(4.7)	(3.4)	7.7
Interest expense, net									(11.2)	(10.4)	(9.2)
Other (expense) income									0.0	0.0	2.3
Share of affiliates' earnings (pre-tax)									94.5	60.5	58.4
Segment profit (loss)									62.4	38.7	56.3
Disposition Gains on Owned Assets									0.0	0.0	1.8
Nonoperating Income, Residual Sharing Income									1.5	1.1	9.6
Nonremarketing Disposition Gain (Loss)									0.0	0.0	0.0
Asset Impairment Charges									(6.2)	(4.5)	(3.7)
Selected Balance Sheet Data
Investments in affiliated companies					464.3					464.3	434.2
Identifiable assets	653.7				606.8				653.7	606.8	582.8
Capital Expenditures
Portfolio investments and capital additions									0.0	(14.1)	(36.6)
Other [Member]
Profitability
Lease revenue									0.0	0.0	0.0
Marine operating revenue									0.0	0.0	0.0
Other revenue									0.0	0.0	0.0
Total Revenues									0.0	0.0	0.0
Maintenance expense									0.0	0.0	0.0
Marine operating expense									0.0	0.0	0.0
Depreciation									0.0	0.0	0.0
Operating lease expense									0.0	0.0	0.0
Other operating expense									0.0	0.0	0.0
Total Expenses									0.0	0.0	0.0
Net gain on asset dispositions									0.0	0.0	0.0
Interest expense, net									5.8	8.6	8.5
Other (expense) income									(3.2)	(9.5)	(7.1)
Share of affiliates' earnings (pre-tax)									0.0	0.0	0.0
Segment profit (loss)									2.6	(0.9)	1.4
Disposition Gains on Owned Assets									0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									0.0	0.0	0.0
Asset Impairment Charges									0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0				0.0				0.0	0.0	0.0
Identifiable assets	$ 206.9				$ 112.3				206.9	112.3	305.0
Capital Expenditures
Portfolio investments and capital additions									(4.9)	(23.4)	(1.0)
Parent [Member]
Profitability
Income tax benefit									66.4	44.9	(231.7)
Adler Funding Llc [Member]
Profitability
Asset Impairment Charges									$ 0.0	$ 0.0	$ (3.0)
Capital Expenditures
Noncontrolling Interest, Ownership Percentage by Parent	12.50%								12.50%
Adler Funding Llc [Member] | Rail North America [Member]
Selected Balance Sheet Data
Investments in affiliated companies	$ 0.2								$ 0.2
Cardinal Marine [Domain]
Capital Expenditures
Noncontrolling Interest, Ownership Percentage by Parent												50.00%