SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	$ 14,120	$ 11,914	$ 10,232
Additions Charged to Costs and Expenses	26,564	2,345	1,682
Deductions	(14)	(139)
Balance at End of Year	$ 40,670	14,120	11,914
Number of seats on aircraft | item	50
Allowance for inventory obsolescence
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	$ 13,933	11,588	10,138
Additions Charged to Costs and Expenses	26,564	2,345	1,450
Balance at End of Year	40,497	13,933	11,588
Allowance for doubtful accounts receivable
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year	187	326	94
Additions Charged to Costs and Expenses			232
Deductions	(14)	(139)
Balance at End of Year	$ 173	$ 187	$ 326