Financial Instruments and Risk Management (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Fuel, Transportation [Member] gal	Dec. 31, 2011 Fuel, Transportation [Member] gal	Jun. 30, 2012 Heating Oil [Member]
Derivative [Line Items]
Into-plane fuel cost	$ 116,600,000	$ 107,000,000	$ 227,500,000	$ 192,600,000
Changes in value and settlements of fuel hedge contracts	3,600,000	300,000	1,400,000	(4,300,000)
Aircraft fuel expense	120,233,000	107,322,000	228,958,000	188,234,000
Realized gains (losses) from derivatives	(2,500,000)	3,100,000	(37,000)	7,200,000
Unrealized gains (losses) from derivatives	$ (1,100,000)	$ (3,500,000)	$ (1,400,000)	$ (2,900,000)
Nonmonetary notional amount (in gallons)					7,500,000	13,450,000
Nonmonetary notional amount, percent of required need, coverage (as a percent)					19.00%	9.00%	72.00%
Weighted average floor price (in dollars per gallon)					2.95	2.81
Weighted average ceiling price (in dollars per gallon)					3.16	2.99