Contingencies - Narrative (Details)		9 Months Ended
	Jun. 09, 2015 USD ($)	Sep. 30, 2018 USD ($) lawsuit
Accrued liabilities
Loss Contingencies [Line Items]
Total accruals		$ 25,900,000
Highway Products Litigation | False Claims Act, USA
Loss Contingencies [Line Items]
Damages awarded by jury verdict	$ 175,000,000
Total amount of judgment entered by the District Court	682,400,000
Damages awarded by jury verdict, automatically trebled under the Act	525,000,000
Civil penalties included in judgment entered by the District Court	138,400,000
Costs and attorney's fees included in judgment entered by the District Court	$ 19,000,000
Total accruals		0
Highway Products Litigation | State, county, and municipal actions
Loss Contingencies [Line Items]
Total accruals		$ 0
Number of additional separate state qui tam actions filed | lawsuit		13
Highway Products Litigation | Class Action, Shareholder
Loss Contingencies [Line Items]
Total accruals		$ 0
Environmental and workplace matters
Loss Contingencies [Line Items]
Total accruals		2,900,000
Minimum
Loss Contingencies [Line Items]
Range of possible loss		4,200,000
Maximum
Loss Contingencies [Line Items]
Range of possible loss		$ 27,400,000