Note 3 - Revenue and Business Segments (Details Textual)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Number of Operating Segments			5
Number of Reportable Segments			4
Customer Contract Term			1 year
Dedicated [Member]
Depreciation, Depletion and Amortization, Total	$ 7,400,000	$ 5,400,000	$ 14,100,000	$ 10,800,000
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	13,100,000	14,400,000	$ 26,600,000	29,000,000
Intermodal [Member]
Depreciation, Depletion and Amortization, Total	1,400,000	1,100,000	2,700,000	2,200,000
Brokerage [Member]
Depreciation, Depletion and Amortization, Total	$ 300,000	$ 344,000	$ 623,000	$ 678,000