Summary of Significant Accounting Policies (Schedule of Effects of Change in Accounting Estimate) (Details) - Change in accounting method accounted for as change in estimate [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in Accounting Estimate [Line Items]
Change in Accounting Estimate, Description	During fourth quarter 2016, due to the weak used truck market, we reduced the estimated life of certain trucks to more rapidly depreciate the trucks to their residual values.
Depreciation	$ 3.4	$ 4.1