Contingencies and Commitments, Certain Significant Risks and Uncertainties (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Customers Distributor	Dec. 31, 2016 Customers	Dec. 31, 2015 Customers
Guaranties [Abstract]
Issued guaranties	$ 21,554
Maximum [Member]
Guaranties [Abstract]
Guarantor obligations, expiration period	4 years
Performance Bonds [Member]
Guaranties [Abstract]
Issued guaranties	$ 11,316
Marine Transportation [Member]
Certain Significant Risks and Uncertainties [Abstract]
Percentage of inland revenue	75.00%
Marine Transportation [Member] | Minimum [Member]
Certain Significant Risks and Uncertainties [Abstract]
Range of renewal options under term contracts	1 year
Marine Transportation [Member] | Maximum [Member]
Certain Significant Risks and Uncertainties [Abstract]
Range of renewal options under term contracts	5 years
Marine Transportation [Member] | Customers [Member]
Certain Significant Risks and Uncertainties [Abstract]
Percentage of costal revenue	80.00%
Customer relationship period	40 years
Number of single customers accounting more than 10% of segment revenue | Customers	0	0	0
Distribution and Services [Member]
Certain Significant Risks and Uncertainties [Abstract]
Number of off-highway top distributors | Distributor	5
Services segment's relationship term	52 years
Distribution and Services [Member] | Customers [Member]
Certain Significant Risks and Uncertainties [Abstract]
Number of single customers accounting more than 10% of segment revenue | Customers	0	0	0
Letters Of Credit [Member]
Guaranties [Abstract]
Issued guaranties	$ 10,238