Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable allowance	$ 1,456	$ 1,345
Drivers' advances and other receivables, allowance	$ 556	$ 519
Treasury stock, shares (in shares)		23,656
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares issued (in shares)	15,979,703	15,922,879
Common stock, shares outstanding (in shares)	15,979,703	15,899,223
Common Class B [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	5,000,000	5,000,000
Common stock, shares issued (in shares)	2,350,000	2,350,000
Common stock, shares outstanding (in shares)	2,350,000	2,350,000