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Schedule II - Valuation and Qualifying Accounts and Reserves | 12 Months Ended
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Dec. 31, 2020
Notes to Financial Statements |
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] | SCHEDULE II MARTEN TRANSPORT, LTD. Valuation and Qualifying Accounts and Reserves (In thousands)
|  | Balance at |  |  | Charged to |  |  |  |  |  |  |  |  |  |
|  | Beginning of |  |  | Costs and |  |  |  |  |  |  |  | Balance at |
Description |  | Year |  |  | Expenses |  |  | Deductions |  |  |  | End of Year |
Insurance and claims accruals: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Year ended December 31, 2020 |  | $ | 31,729 |  |  | $ | 64,276 |  |  | $ | (56,410 | )(1) |  |  | $ | 39,595 |
Year ended December 31, 2019 |  |  | 28,103 |  |  |  | 56,075 |  |  |  | (52,449 | )(1) |  |  |  | 31,729 |
Year ended December 31, 2018 |  |  | 26,177 |  |  |  | 56,122 |  |  |  | (54,196 | )(1) |  |  |  | 28,103 |
Allowance for doubtful accounts: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Year ended December 31, 2020 |  |  | 382 |  |  |  | 220 |  |  |  | (254 | )(2) |  |  |  | 348 |
Year ended December 31, 2019 |  |  | 348 |  |  |  | 65 |  |  |  | (31 | )(2) |  |  |  | 382 |
Year ended December 31, 2018 |  |  | 300 |  |  |  | 163 |  |  |  | (115 | )(2) |  |  |  | 348 |
(1) | Claims payments
(2) | Write-off of bad debts, net of recoveries
See report of independent registered public accounting firm.

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- Definition The entire disclosure for valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690 + Details
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