Financial Data of Business Segments (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment									$ 33,600,000	$ 18,000,000.0	$ 10,800,000
Number of business segments | Segment									3
Profitability
Lease revenue									$ 1,087,500,000	1,088,500,000	1,083,700,000
Marine operating revenue									15,600,000	8,200,000	14,300,000
Other revenue									106,100,000	105,400,000	77,100,000
Total Revenues	$ 304,900,000	$ 304,400,000	$ 300,500,000	$ 299,400,000	$ 300,500,000	$ 298,800,000	$ 297,500,000	$ 305,300,000	1,209,200,000	1,202,100,000	1,175,100,000
Maintenance expense									315,500,000	314,400,000	299,200,000
Marine operating expense									19,700,000	18,900,000	16,800,000
Depreciation									330,500,000	321,300,000	311,300,000
Operating lease expense									49,300,000	54,400,000	49,600,000
Other operating expense									35,300,000	31,300,000	33,100,000
Total Expenses									750,300,000	740,300,000	710,000,000.0
Net gain on asset dispositions									41,700,000	51,600,000	72,700,000
Interest Income (Expense), Net									(190,300,000)	(180,500,000)	(162,900,000)
Other (expense) income									(13,000,000.0)	(7,300,000)	(21,700,000)
Share of affiliates' earnings (pre-tax)									95,800,000	94,500,000	61,100,000
Segment profit (loss)									393,100,000	420,100,000	414,300,000
SG&A									172,000,000.0	180,400,000	182,500,000
Income tax benefit									37,300,000	40,900,000	30,500,000
Income from continuing operations					42,100,000	37,200,000	60,300,000	41,200,000	150,200,000	180,800,000	190,500,000
Disposition Gains on Owned Assets									39,400,000	58,600,000	64,700,000
Nonoperating Income, Residual Sharing Income									2,500,000	1,900,000	2,500,000
Nonremarketing Disposition Gain (Loss)									100,000	(2,300,000)	14,500,000
Asset Impairment Charges									(300,000)	(6,600,000)	(9,000,000.0)
Selected Balance Sheet Data
Investments in affiliated companies	584,700,000				512,600,000				584,700,000	512,600,000	464,500,000
Assets of Continuing Operations	8,937,600,000				7,994,000,000.0				8,937,600,000	7,994,000,000.0	7,318,900,000
Total Assets of Discontinued Operations	0				291,100,000				0	291,100,000	297,800,000
Identifiable assets	8,937,600,000				8,285,100,000				8,937,600,000	8,285,100,000	7,318,900,000
Capital Expenditures
Portfolio investments and capital additions									(1,064,000,000.0)	(722,800,000)	(927,600,000)
Total Discontinued Operations, Net of Taxes	0	(300,000)	2,300,000	(900,000)	14,500,000	7,900,000	7,700,000	300,000	1,100,000	30,400,000	20,800,000
Net Income	17,800,000	$ 47,900,000	$ 39,300,000	$ 46,300,000	56,600,000	$ 45,100,000	$ 68,000,000.0	$ 41,500,000	151,300,000	211,200,000	211,300,000
Rail North America [Member]
Profitability
Lease revenue									838,300,000	868,300,000	873,400,000
Marine operating revenue									0	0	0
Other revenue									95,800,000	96,200,000	68,100,000
Total Revenues									934,100,000	964,500,000	941,500,000
Maintenance expense									264,700,000	267,900,000	254,700,000
Marine operating expense									0	0
Depreciation									258,600,000	256,900,000	248,500,000
Operating lease expense									49,300,000	54,400,000	49,600,000
Other operating expense									27,300,000	23,900,000	27,300,000
Total Expenses									599,900,000	603,100,000	580,100,000
Net gain on asset dispositions									38,300,000	54,600,000	76,300,000
Interest Income (Expense), Net									(139,900,000)	(134,500,000)	(125,200,000)
Other (expense) income									(4,900,000)	(5,300,000)	(5,200,000)
Share of affiliates' earnings (pre-tax)									(100,000)	0	600,000
Segment profit (loss)									227,600,000	276,200,000	307,900,000
Disposition Gains on Owned Assets									38,800,000	58,500,000	64,700,000
Nonoperating Income, Residual Sharing Income									400,000	400,000	1,400,000
Nonremarketing Disposition Gain (Loss)									(600,000)	(3,900,000)	10,800,000
Asset Impairment Charges									(300,000)	(400,000)	(600,000)
Selected Balance Sheet Data
Investments in affiliated companies					200,000					200,000	200,000
Assets of Continuing Operations	5,944,400,000				5,646,700,000				5,944,400,000	5,646,700,000
Total Assets of Discontinued Operations					0					0	0
Identifiable assets											5,236,600,000
Capital Expenditures
Portfolio investments and capital additions									(642,000,000.0)	(502,200,000)	(737,400,000)
Rail International [Member]
Profitability
Lease revenue									248,400,000	219,200,000	209,300,000
Marine operating revenue									0	0	0
Other revenue									9,700,000	8,500,000	8,200,000
Total Revenues									258,100,000	227,700,000	217,500,000
Maintenance expense									50,800,000	46,500,000	44,500,000
Marine operating expense									0	0	0
Depreciation									66,600,000	57,800,000	55,500,000
Operating lease expense									0	0	0
Other operating expense									7,500,000	6,800,000	5,800,000
Total Expenses									124,900,000	111,100,000	105,800,000
Net gain on asset dispositions									1,200,000	1,700,000	(200,000)
Interest Income (Expense), Net									(45,900,000)	(40,600,000)	(35,900,000)
Other (expense) income									(5,000,000.0)	1,200,000	(7,000,000.0)
Share of affiliates' earnings (pre-tax)									0	0	0
Segment profit (loss)									83,500,000	78,900,000	68,600,000
Disposition Gains on Owned Assets									500,000	100,000	0
Nonoperating Income, Residual Sharing Income									0	0	0
Nonremarketing Disposition Gain (Loss)									700,000	1,600,000	3,700,000
Asset Impairment Charges									0	0	(3,900,000)
Selected Balance Sheet Data
Investments in affiliated companies					0					0	0
Assets of Continuing Operations	1,851,800,000				1,486,700,000				1,851,800,000	1,486,700,000
Total Assets of Discontinued Operations					0					0	0
Identifiable assets											1,363,200,000
Capital Expenditures
Portfolio investments and capital additions									(216,000,000.0)	(215,700,000)	(152,700,000)
Portfolio Management [Member]
Profitability
Lease revenue									800,000	1,000,000.0	1,000,000.0
Marine operating revenue									15,600,000	8,200,000	14,300,000
Other revenue									600,000	700,000	800,000
Total Revenues									17,000,000.0	9,900,000	16,100,000
Maintenance expense									0	0	0
Marine operating expense									19,700,000	18,900,000	16,800,000
Depreciation									5,300,000	6,600,000	7,300,000
Operating lease expense									0	0	0
Other operating expense									500,000	600,000	0
Total Expenses									25,500,000	26,100,000	24,100,000
Net gain on asset dispositions									2,200,000	(4,700,000)	(3,400,000)
Interest Income (Expense), Net									(12,200,000)	(11,200,000)	(10,400,000)
Other (expense) income									0	0	0
Share of affiliates' earnings (pre-tax)									95,900,000	94,500,000	60,500,000
Segment profit (loss)									77,400,000	62,400,000	38,700,000
Disposition Gains on Owned Assets									100,000	0	0
Nonoperating Income, Residual Sharing Income									2,100,000	1,500,000	1,100,000
Nonremarketing Disposition Gain (Loss)									0	0	0
Asset Impairment Charges									0	(6,200,000)	(4,500,000)
Selected Balance Sheet Data
Investments in affiliated companies					512,400,000					512,400,000	464,300,000
Assets of Continuing Operations	706,100,000				653,700,000				706,100,000	653,700,000	606,800,000
Total Assets of Discontinued Operations					0					0	0
Capital Expenditures
Portfolio investments and capital additions									(500,000)	0	(14,100,000)
Other [Member]
Profitability
Lease revenue									0	0	0
Marine operating revenue									0	0	0
Other revenue									0	0	0
Total Revenues									0	0	0
Maintenance expense									0	0	0
Marine operating expense									0	0	0
Depreciation									0	0	0
Operating lease expense									0	0	0
Other operating expense									0	0	0
Total Expenses									0	0	0
Net gain on asset dispositions									0	0	0
Interest Income (Expense), Net									7,700,000	5,800,000	8,600,000
Other (expense) income									(3,100,000)	(3,200,000)	(9,500,000)
Share of affiliates' earnings (pre-tax)									0	0	0
Segment profit (loss)									4,600,000	2,600,000	(900,000)
Disposition Gains on Owned Assets									0	0	0
Nonoperating Income, Residual Sharing Income									0	0	0
Nonremarketing Disposition Gain (Loss)									0	0	0
Asset Impairment Charges									0	0	0
Selected Balance Sheet Data
Investments in affiliated companies					0					0	0
Assets of Continuing Operations	$ 435,300,000				206,900,000				435,300,000	206,900,000
Total Assets of Discontinued Operations					0					0	0
Identifiable assets											112,300,000
Capital Expenditures
Portfolio investments and capital additions									(205,500,000)	(4,900,000)	(23,400,000)
Parent [Member]
Profitability
Income tax benefit									$ 70,900,000	58,900,000	$ 41,300,000
Adler Funding Llc [Member]
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				$ 200,000				$ 0	$ 200,000