Commitments and Contingencies (Commitments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Long-term Purchase Commitment [Line Items]
aircraft purchase deposit	$ 25,800		$ 25,800
Long-term Purchase Commitment, Amount			176,200
total government grant awarded	75,400		75,400
government grant cash received	75,400		75,400
Income Tax (Expense) Benefit, Continuing Operations, Government Grants	21,726	$ 0	31,547	$ 0
unrecognized government grants received	$ 43,900		$ 43,900