Commitments and Contingencies (Commitments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Long-term Purchase Commitment [Line Items]
aircraft purchase deposit	$ 7,600
Long-term Purchase Commitment, Amount	172,800
total government grant awarded		$ 37,400	$ 75,800
Income Tax (Expense) Benefit, Continuing Operations, Government Grants	28,030	$ 0
unrecognized government grants received	$ 37,900