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Valuation and Qualifying Accounts (Notes)
 12 Months Ended
Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Valuation and Qualifying Accounts
(in thousands)Balance at Beginning of YearChanges Charged to Statement of Income AccountsWrite Offs (net of recoveries)Balance at End of Year
Allowance for expendable parts and supplies
For the Year Ended December 31, 2021$4,323 $1,718 $— $6,041 
For the Year Ended December 31, 20202,748 1,575 — 4,323 
For the Year Ended December 31, 2019 (1)
14,410 2,257 (13,919)2,748 
(1) Increase in write offs mostly related to disposal of MD-80 fleet parts in 2019.