Contingencies (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Mar. 13, 2015 crash_tests	Mar. 11, 2015 guardrails	Feb. 06, 2015 crash_tests
Contingencies (Textual) [Abstract]
Minimum possible loss	$ 3,500,000
Maximum possible loss	23,700,000
Total accruals	25,800,000
Revenue	1,626,700,000	1,460,500,000
Highway Products Litigation
Contingencies (Textual) [Abstract]
Number of additional crash tests requested			8
Number of additional crash tests passed, first installation height							4
Number of additional crash tests passed, second installation height					4
Number of ET Plus devices field measured by FHWA engineers, more than						1,000
Number of states that have removed product from qualified products list	41
Number of class action lawsuits	3
Highway Products Litigation | ET Plus
Contingencies (Textual) [Abstract]
Revenue			35,100,000	46,000,000
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	13
Number of tank cars manufactured by the Company	35
Number of tank cars involved in derailment	72
Environmental and workplace matters
Contingencies (Textual) [Abstract]
Total accruals	5,200,000
False Claims Act | Highway Products Litigation
Contingencies (Textual) [Abstract]
Damages awarded by jury verdict	175,000,000
Damages awarded by jury verdict, automatically trebled under the Act	525,000,000
Minimum possible loss	525,000,000
Maximum possible loss	709,000,000
Potential amount of bond required in excess of final judgment	20.00%
Total accruals	0
False Claims Act | Minimum | Highway Products Litigation
Contingencies (Textual) [Abstract]
Civil penalties per violation, at the discretion of the District Court	5,500
Civil penalties, at the discretion of the District Court	5,500
False Claims Act | Maximum | Highway Products Litigation
Contingencies (Textual) [Abstract]
Civil penalties per violation, at the discretion of the District Court	11,000
Civil penalties, at the discretion of the District Court	184,000,000
Class Action, Illinois | Highway Products Litigation
Contingencies (Textual) [Abstract]
Number of other counties claimed as parties to class action suit	101
Class Action, Canada | Highway Products Litigation
Contingencies (Textual) [Abstract]
Compensatory damages sought	400,000,000
Punitive damages sought	$ 100,000,000