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Valuation and Qualifying Accounts (Tables) | 12 Months Ended
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Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |
Schedule Of Valuation And Qualifying Accounts |
(in thousands) | Balance at Beginning of Year |  | Changes Charged to Statement of Income Accounts |  | Write Offs (net of recoveries) |  | Balance at End of Year
Allowance for expendable parts and supplies |  |  |  |  |  |  |
For the Year Ended December 31, 2020 | $ | 2,748 |  |  | $ | 1,575 |  |  | $ | — |  |  | $ | 4,323 |
For the Year Ended December 31, 2019 (1) | 14,410 |  |  | 2,257 |  |  | (13,919) |  |  | 2,748 |
For the Year Ended December 31, 2018 | 13,756 |  |  | 2,624 |  |  | (1,970) |  |  | 14,410 |
(1) Increase in write offs mostly related to disposal of MD-80 fleet parts in 2019.

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