Note 3 - Revenue and Business Segments (Details Textual)	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2018	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Number of Operating Segments				5
Number of Reportable Segments			4	4
Customer Contract Term				1 year
Dedicated [Member]
Depreciation, Depletion and Amortization, Total	$ 7,800,000	$ 5,600,000		$ 21,900,000	$ 16,400,000
Dedicated [Member] | Minimum [Member]
Customer Contract Term				3 years
Dedicated [Member] | Maximum [Member]
Customer Contract Term				5 years
Truckload [Member]
Depreciation, Depletion and Amortization, Total	12,800,000	14,100,000		$ 39,400,000	43,100,000
Intermodal [Member]
Depreciation, Depletion and Amortization, Total	1,400,000	1,200,000		4,100,000	3,400,000
Brokerage [Member]
Depreciation, Depletion and Amortization, Total	$ 337,000	$ 328,000		$ 960,000	$ 1,000,000