Leases and Prepaid Maintenance Deposits - Operating Leases (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 aircraft_engine	Dec. 31, 2011	Dec. 31, 2010
Operating Leased Assets [Line Items]
Total rental expense	$ 172,400,000	$ 139,100,000	$ 122,700,000
Rental expense charged to operations for aircraft and engine operating leases	143,572,000	116,485,000	101,345,000
Prepaid aircraft maintenance to lessors, total	198,500,000	168,800,000
Supplemental rent	2,000,000	1,500,000	0
Number of spare aircraft engines entered into sale and leaseback agreement	2
Other current assets
Operating Leased Assets [Line Items]
Prepaid aircraft maintenance to lessors, current	$ 76,100,000	$ 48,200,000
Aircraft
Operating Leased Assets [Line Items]
Number of aircraft and spare engines financed under operating leases	45
Number of aircraft and spare engines financed under operating leases with a variable rate	5
Basis for aircraft financed under operating leases with a variable rate	LIBOR
Number of aircraft leaes available for renewal	17
Aircraft operating leases, renewal term	3 years
Aircraft operating leases, period before renewal	10 years
Aircraft | Minimum
Operating Leased Assets [Line Items]
Operating leases, term	3 years
Aircraft | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	12 years
Other leased equipment and property | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	20 years
Spare engines
Operating Leased Assets [Line Items]
Number of aircraft and spare engines financed under operating leases	8
Spare engines | Minimum
Operating Leased Assets [Line Items]
Operating leases, term	7 years
Spare engines | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	12 years