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Note 1 - Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Number of Operating Segments	5
Number of Dry Vans	1,600
Loss on Deposits Above FDIC Amount	$ 0
Letters of Credit Outstanding, Amount	$ 14,600,000	$ 12,900,000
Number of Reportable Segments	4
Assets, Total	$ 753,904,000	690,403,000
Liabilities, Total	$ 177,950,000	$ 164,903,000
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Assets, Total				$ 1,000,000
Liabilities, Total				$ 1,000,000
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Walmart [Member]
Concentration Risk, Percentage	15.00%	19.00%	17.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | The Coca-Cola Company [Member]
Concentration Risk, Percentage	13.00%
Sales Revenue, Net [Member] | Geographic Concentration Risk [Member] | UNITED STATES
Concentration Risk, Percentage	99.00%	99.00%	99.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Walmart [Member]
Concentration Risk, Percentage	12.00%	15.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | The Coca-Cola Company [Member]
Concentration Risk, Percentage	7.00%
Uninsured Risk [Member] | Auto Liability Claim [Member]
Loss Contingency Range Possible Loss Per Claim	$ 1,000,000
Uninsured Risk [Member] | Workers Compensation Liability Claim [Member]
Loss Contingency Range Possible Loss Per Claim	750,000
Insurance Claims [Member]
Letters of Credit Outstanding, Amount	14,600,000
Supplies and Maintenance Costs [Member]
Amortization, Total	$ 7,000,000	$ 7,100,000	$ 6,900,000
Tractor [Member]
Replacement Of Equipment Period After Purchase	3 years 255 days
Property, Plant and Equipment, Useful Life	5 years
Property, Plant and Equipment, Salvage Value, Percentage	25.00%
Trailer [Member]
Replacement Of Equipment Period After Purchase	5 years 182 days
Property, Plant and Equipment, Useful Life	7 years
Property, Plant and Equipment, Salvage Value, Percentage	35.00%
Tires In Service [Member]
Property, Plant and Equipment, Useful Life		2 years

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