Financial Instruments and Risk Management (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Fuel [Member] gal	Dec. 31, 2012 Fuel [Member] gal
Investments, All Other Investments [Abstract]
Into-plane fuel cost	$ 129,375,000	$ 116,622,000	$ 258,088,000	$ 227,539,000
Settlement losses (gains)	113,000	2,488,000	(315,000)	37,000
Unrealized mark-to-market losses (gains)	5,763,000	1,123,000	9,144,000	1,382,000
Aircraft fuel	135,251,000	120,233,000	266,917,000	228,958,000
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 800,000		$ 800,000
Nonmonetary notional amount (in gallons)					7,700,000	7,800,000
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage, Remaining Fiscal Year					8.70%
Nonmonetary notional amount, percent of required need, coverage, August through October of current fiscal year					71.00%
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage, Next Fiscal Quarter					17.00%
Nonmonetary notional amount, percent of required need, coverage, next fiscal year						4.60%
Weighted average ceiling price (in dollars per gallon)					2.95	3.09
Weighted average floor price (in dollars per gallon)					2.68	2.84