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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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