Special Charges (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) aircraft_engine	Sep. 30, 2016 USD ($) aircraft_engine	Sep. 30, 2017 USD ($) aircraft_engine	Sep. 30, 2016 USD ($) aircraft
Property, Plant and Equipment [Line Items]
Purchase of property and equipment			$ 428,061	$ 447,455
Special charges	$ 7,853	$ 7,355	$ 12,629	$ 31,609
Spare Engines [Member] | Spare Engines [Member]
Property, Plant and Equipment [Line Items]
Number of previously leased engines | aircraft_engine			1
Purchase price			$ 8,100
Purchase of property and equipment			3,800
Value of noncash consideration			4,300
Fair value of assets acquired			3,100
Special charges			4,800
Spare Engines [Member] | Spare Engines [Member] | Other Non-Cash Items [Member]
Property, Plant and Equipment [Line Items]
Value of noncash consideration			$ 200
Aircraft [Member]
Property, Plant and Equipment [Line Items]
Number of previously leased engines | aircraft_engine	1		1
Aircraft [Member] | Airbus A319 [Member]
Property, Plant and Equipment [Line Items]
Number of previously leased engines		3		6
Purchase price	$ 20,000	$ 58,800		$ 124,700
Purchase of property and equipment	12,600	58,100		91,900
Value of noncash consideration	7,400	700		32,800
Fair value of assets acquired	11,900	38,200		79,400
Special charges	7,900	7,400		31,600
Aircraft [Member] | Airbus A319 [Member] | Other Non-Cash Items [Member]
Property, Plant and Equipment [Line Items]
Value of noncash consideration	$ 200	$ 13,200		$ 13,700