Property and Equipment (Schedule of Property and Equipment) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 1,855,689	$ 1,731,983
Accumulated depreciation	(781,450)	(730,991)
Property and equipment, net	1,074,239	1,000,992
Flight Equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	1,633,793	1,541,872
Ground equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	50,734	49,229
facilities, leasehold improvements and office equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	27,382	27,364
Construction in Progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 143,780	$ 113,518