SCHEDULE II —VALUATION AND QUALIFYING ACCOUNTS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) item
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	$ 17,255	$ 40,670	$ 14,120
Additions Charged to Costs and Expenses	5,044		26,564
Deductions		(23,415)	(14)
Balance at End of Year	22,299	17,255	$ 40,670
Number of seats on aircraft | item			50
Allowance for inventory obsolescence
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	17,098	40,497	$ 13,933
Additions Charged to Costs and Expenses	5,043		26,564
Deductions		(23,399)
Balance at End of Year	22,141	17,098	40,497
Allowance for doubtful accounts receivable
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	157	173	187
Additions Charged to Costs and Expenses	1
Deductions		(16)	(14)
Balance at End of Year	$ 158	$ 157	$ 173