Supplemental Cash Flow Information Significant Non-Cash Investing Activities(Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 USD ($)
Outstanding receivables from outside parties for the funding of capital expenditures		$ 10.7	$ 23.0		$ 17.7
Purchases of property and equipment accrued in accounts payable	$ 20.0	$ 16.4	$ 26.2
Common Stock [Member] | Class A Common Stock [Member]
Stock issued during period, shares | shares	238,201
Settlement of Freightliner Deferred Consideration [Member]
Notes Payable				£ 6.3	8.6
Notes Payable, Fair Value Disclosure				£ 5.7	$ 7.7
Settlement of Freightliner Deferred Consideration [Member] | Common Stock [Member] | Class A Common Stock [Member]
Stock issued during period, shares | shares	238,201
Settlement of Freightliner Deferred Consideration [Member] | Additional Paid-in Capital [Member]
Conversion of Stock, Amount Issued	$ 17.5