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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Letters of Credit Outstanding, Amount |  | $ 12,900,000 |  |
Income Tax Expense (Benefit) |  | $ (33,811,000) | $ 23,602,000 | $ 24,946,000
Number of Operating Segments |  | 5 |  |
Number of Reportable Segments |  | 4 |  |
Accounting Standards Update 2016-09 [Member] |  |  |  |
Income Tax Expense (Benefit) |  | $ (176,000) |  |
Accounting Standards Update 2014-09 [Member] | Scenario, Forecast [Member] |  |  |  |
Cumulative Effect on Retained Earnings, before Tax | $ 485,000 |  |  |
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Walmart [Member] |  |  |  |
Concentration Risk, Percentage |  | 19.00% | 17.00% | 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 |  | 15.00% | 17.00% |
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 |  | 12,900,000 |  |
Supplies and Maintenance Costs [Member] |  |  |  |
Amortization |  | $ 7,100,000 | $ 6,900,000 | $ 6,300,000
Tractor [Member] |  |  |  |
Replacement Of Equipment Period After Purchase |  | 3 years 292 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 255 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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