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Leases and Capacity Purchase Agreements - Additional Information Related to Leases (Details)
Dec. 31, 2020
Dec. 31, 2019
Leases [Abstract]    
Weighted-average remaining lease term - operating leases 11 years 11 years
Weighted-average remaining lease term - finance leases 4 years 6 years
Weighted-average discount rate - operating leases 5.10% 5.20%
Weighted-average discount rate - finance leases 4.40% 5.70%