Special Charges (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) aircraft_engine	Jun. 30, 2016 USD ($) aircraft
Property, Plant and Equipment [Line Items]
Purchase of property and equipment			$ 269,519	$ 303,175
Special charges	$ 0	$ 8,052	$ 4,776	$ 24,254
Airbus A319 [Member] | Aircraft [Member]
Property, Plant and Equipment [Line Items]
Number of previously leased engines | aircraft				3
Purchase price				$ 65,900
Purchase of property and equipment				33,800
Value of noncash consideration				32,100
Fair value of assets acquired				41,200
Special charges				24,300
Airbus A319 [Member] | Aircraft [Member] | Other Non-Cash Items [Member]
Property, Plant and Equipment [Line Items]
Value of noncash consideration				$ 400
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