Note 4 - Segment Reporting (Details Textual) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Number of Reportable Segments				2
Revenues, Total		$ 135,381	$ 107,358	$ 260,394	$ 209,028
Trucking [Member]
Revenues, Total		85,569	71,545	164,302	141,825
Trucking [Member] | Operating Segments [Member]
Revenues, Total	[1]	85,685	71,731	164,531	142,202
Trucking [Member] | Foreign Countries [Member] | Operating Segments [Member]
Revenues, Total		$ 11,000	$ 9,100	$ 20,900	$ 17,900

[1] Includes foreign revenue of $11.0 million and $20.9 million for the three and six months ended June 30, 2018, respectively, and $9.1 million and $17.9 million for the three and six months ended June 30, 2017, respectively. All foreign revenue is collected in U.S. dollars.