Earnings Per Common Share Sales of Unregistered Securities (Details) - Class A Common Stock [Member] - Common Stock [Member]	12 Months Ended
Dec. 31, 2017 shares
Shares issued upon buyout of deferred consideration	238,201
Settlement of Freightliner Deferred Consideration [Member]
Shares issued upon buyout of deferred consideration	238,201

Number of shares of stock issued attributable to transactions classified as other.

No definition available.

Name:	us-gaap_StockIssuedDuringPeriodSharesOther
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration