Commitments and Contingencies (Commitments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Long-term Purchase Commitment [Line Items]
aircraft purchase deposit	$ 11,300		$ 11,300
Long-term Purchase Commitment, Amount			230,200
total government grant awarded	75,400		75,400
government grant cash received	37,700		37,700
Income Tax (Expense) Benefit, Continuing Operations, Government Grants	9,821	$ 0	9,821	$ 0
unrecognized government grants received	$ 27,900		$ 27,900