Partially-Owned Leasing Subsidiaries - Narrative (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) board_member subsidiary	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		5.00%
Partially-owned subsidiaries
Noncontrolling Interest [Line Items]
Trinity guarantees of subsidiary-related activities \| $	$ 0
Railcar Leasing and Management Services Group \| Partially-owned subsidiaries
Noncontrolling Interest [Line Items]
Number of subsidiaries \| subsidiary	2
Number of board members \| board_member	7
Number of TILC designated board members \| board_member	2
Partially-owned subsidiaries \| Railcar Leasing and Management Services Group
Noncontrolling Interest [Line Items]
Carrying value of investment in partially-owned subsidiaries \| $	$ 188,700,000
Weighted average ownership	38.00%
Weighted average ownership interest by institutional investors	62.00%

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Number of subsidiaries.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=108788376&loc=SL6759159-111685

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