Note 1 - Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Lease, Right-of-Use Asset	$ 39,100
Operating Lease, Liability, Current	14,622
Operating Lease, Liability, Noncurrent	25,541
Operating Lease, Liability, Total	$ 40,163
Tractors [Member]
Property, Plant and Equipment, Useful Life	5 years
Property, Plant and Equipment, Salvage Value, Percentage	15.00%
Refrigerated Trailers [Member]
Property, Plant and Equipment, Useful Life	7 years
Dry Van Trailers [Member]
Property, Plant and Equipment, Useful Life	10 years
Property, Plant and Equipment, Salvage Value, Percentage	25.00%
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset		$ 40,200
Operating Lease, Liability, Current		14,600
Operating Lease, Liability, Noncurrent		25,600
Operating Lease, Liability, Total		$ 41,000