Fuel Derivatives Outstanding (Detail)	Feb. 29, 2012 bbl
Fuel Derivatives 2012 Third Quarter Maturity
Derivative [Line Items]
Barrels	1,044,000	[1]
Weighted-Average Floor Price	92	[1]
Weighted-Average Ceiling Price	132	[1]
Percent of Estimated Fuel Consumption	21.00%	[1]
Fuel Derivatives 2012 Fourth Quarter Maturity
Derivative [Line Items]
Barrels	1,044,000	[1]
Weighted-Average Floor Price	92	[1]
Weighted-Average Ceiling Price	132	[1]
Percent of Estimated Fuel Consumption	20.00%	[1]
Fuel Derivatives Second Half 2012
Derivative [Line Items]
Barrels	2,088,000	[1]
Weighted-Average Floor Price	92	[1]
Weighted-Average Ceiling Price	132	[1]
Fuel Derivatives 2013 Maturity
Derivative [Line Items]
Barrels	4,224,000	[1]
Weighted-Average Floor Price	86	[1]
Weighted-Average Ceiling Price	130	[1]
Percent of Estimated Fuel Consumption	20.00%	[1]
Fuel Derivatives 2014 Maturity
Derivative [Line Items]
Barrels	4,224,000	[1]
Weighted-Average Floor Price	79	[1]
Weighted-Average Ceiling Price	127	[1]
Percent of Estimated Fuel Consumption	20.00%	[1]
Fuel Derivatives 2015 Maturity
Derivative [Line Items]
Barrels	4,320,000	[1]
Weighted-Average Floor Price	75	[1]
Weighted-Average Ceiling Price	125	[1]
Percent of Estimated Fuel Consumption	20.00%	[1]

[1] Fuel derivatives mature evenly over each quarter within the above fiscal years.