Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Airplane operating lease period	seven-year
Maximum residual value guarantee	$ 11.1
Fair value of residual value guarantee, fair value of operating lease asset, threshold	$ 14.4
Operating lease, rent expense		$ 40.3	$ 34.8	$ 33.8