Financial Instruments and Risk Management (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Crude Oil [Member] bbl	Dec. 31, 2011 Fuel [Member] gal	Sep. 30, 2012 Heating Oil [Member]
Investments, All Other Investments [Abstract]
Into-plane fuel cost	$ 123,500,000	$ 103,700,000	$ 351,100,000	$ 296,300,000
Realized losses (gains) from derivatives	(600,000)	(200,000)	(500,000)	(7,500,000)
Unrealized losses (gains) from derivatives	(900,000)	1,500,000	400,000	4,400,000
Aircraft fuel expense	$ 122,016,000	$ 104,985,000	$ 350,974,000	$ 293,219,000
Derivative [Line Items]
Nonmonetary notional amount (in units)					90,000	13,450,000
Nonmonetary notional amount, percent of required need, coverage, next fiscal year						9.00%
Nonmonetary notional amount, percent of required need, coverage, remaining fiscal year					10.00%		24.00%
Weighted average floor price (in dollars per unit)					87.35	2.81
Weighted average ceiling price (in dollars per unit)					94.00	2.99