Partially-Owned Leasing Subsidiaries - Narrative (Details)	6 Months Ended
	Jun. 30, 2018 USD ($) board_member subsidiary
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 | $	$ 189,600,000
Weighted average ownership	38.00%
Weighted average ownership interest by institutional investors	62.00%