DERIVATIVE INSTRUMENTS - FAIR VALUE OF HEDGE POSITIONS (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative [Line Items]
Net cash received (paid) to for new positions and settlements	$ 15.9	$ (16.3)	$ (60.5)
B737-800 [Member]
Derivative [Line Items]
Capital Leased Assets, Number of B737-800 Aircraft	6
Not Designated as Hedging Instrument [Member] | Fuel hedge contracts [Member]
Derivative [Line Items]
Average strike price per barrel (in dollars per barrel)	100
Fuel hedge contracts outstanding (in gallons)	421,100,000
Derivatives Maturing 2013 and 2014 [Member] | Not Designated as Hedging Instrument [Member] | Fuel hedge contracts [Member]
Derivative [Line Items]
Average strike price per barrel (in dollars per barrel)	92