Contingencies (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) state guardrails crash_tests	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) state Railcar guardrails crash_tests lawsuit county	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Contingencies (Textual) [Abstract]
Total accruals	$ 24.3		$ 24.3
Revenue	1,676.8	$ 1,485.3	3,303.5	$ 2,945.8
Minimum possible loss	2.9		2.9
Maximum possible loss	$ 21.9		$ 21.9
Highway Products Litigation
Contingencies (Textual) [Abstract]
Number of additional crash tests requested | crash_tests	8		8
Number of additional crash tests passed, first installation height | crash_tests	4		4
Number of additional crash tests passed, second installation height | crash_tests	4		4
Number of ET Plus devices field measured by FHWA engineers, more than | guardrails	1,000		1,000
Number of states that have removed product from qualified products list | state	40		40
Number of class action lawsuits | lawsuit			3
Highway Products Litigation | ET Plus
Contingencies (Textual) [Abstract]
Revenue			$ 0.0		$ 35.1	$ 46.0
Revenues as a percent of consolidated revenue					0.60%	1.10%
Train Derailment
Contingencies (Textual) [Abstract]
Number of tank cars owned by the Company and leased to third party | Railcar			13
Number of tank cars manufactured by the Company | Railcar			35
Number of tank cars involved in derailment | Railcar			72
Environmental and workplace matters
Contingencies (Textual) [Abstract]
Total accruals	$ 4.7		$ 4.7
False Claims Act | Highway Products Litigation
Contingencies (Textual) [Abstract]
Damages awarded by jury verdict			175.0
Total amount of judgment entered by the District Court			682.4
Damages awarded by jury verdict, automatically trebled under the Act			525.0
Civil penalties included in judgment entered by the District Court			138.4
Costs and attorney's fees included in judgment entered by the District Court			19.0
Amount of supersedeas bond posted			686.0
Initial annual premium of supersedeas bond	3.9		3.9
Total accruals	0.0		$ 0.0
Class Action, Illinois | Highway Products Litigation
Contingencies (Textual) [Abstract]
Number of other counties claimed as parties to class action suit | county			101
Class Action, Canada | Highway Products Litigation
Contingencies (Textual) [Abstract]
Compensatory damages sought			$ 400.0
Punitive damages sought			100.0
Class Action | Highway Products Litigation
Contingencies (Textual) [Abstract]
Total accruals	0.0		0.0
Class Action, Shareholder | Highway Products Litigation
Contingencies (Textual) [Abstract]
Total accruals	$ 0.0		$ 0.0