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Financing Arrangements - Equipment Notes (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2021
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2021
USD ($)
Sep. 30, 2020
USD ($)
Aug. 31, 2020
agreement
Debt Disclosure [Abstract]          
Number of long-term financing agreements | agreement         4
Interest expense, debt | $ $ 205 $ 247 $ 665 $ 624