Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Commitment fees	$ 124	$ 127
Amortization of deferred financing costs	5,280	3,435
Total	57,148	41,641
Senior loans
Debt Instrument [Line Items]
Interest expense, debt	18,328	19,759
Junior loans
Debt Instrument [Line Items]
Interest expense, debt	3,035	3,568
Fixed-rate loans
Debt Instrument [Line Items]
Interest expense, debt	8,610	0
2015-1 EETC Class A
Debt Instrument [Line Items]
Interest expense, debt	17,230	11,509
2015-1 EETC Class B
Debt Instrument [Line Items]
Interest expense, debt	4,446	3,243
2017-1 EETC Class AA
Debt Instrument [Line Items]
Interest expense, debt	54	0
2017-1 EETC Class A
Debt Instrument [Line Items]
Interest expense, debt	19	0
2017-1 EETC Class B
Debt Instrument [Line Items]
Interest expense, debt	$ 22	$ 0