Debt - Total interest expense recognized on the Convertible Notes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Unamortized discount	$ 0.3		$ 0.3		$ 8.5
3 7/8% Convertible Subordinated Notes Due 2036 \| Convertible subordinated notes
Debt Instrument [Line Items]
Coupon rate interest	2.8	$ 4.3	7.2	$ 8.7
Amortized debt discount	3.3	4.6	8.2	9.1
Total interest expense recognized on the Convertible Subordinated Notes	6.1	$ 8.9	15.4	$ 17.8
Trinity Rail Leasing 2018 \| 2018 secured railcar equipment notes \| Secured debt
Debt Instrument [Line Items]
Unamortized discount	$ 0.3		$ 0.3		$ 0.0

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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-Section S99
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Amount, after accumulated amortization, of debt discount.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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