Fair Value Measurements, Derivative Instruments and Hedging Activities - Fuel Derivatives Outstanding (Detail)	1 Months Ended
	May 31, 2013 bbl
Fuel Derivatives 2013 Maturity November 2011 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2011-11	[1]
Barrels	1,056,000	[1]
Weighted-Average Floor Price	74	[1]
Weighted-Average Ceiling Price	132	[1]
Fuel Derivatives 2013 Maturity February 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-02	[1]
Barrels	1,056,000	[1]
Weighted-Average Floor Price	98	[1]
Weighted-Average Ceiling Price	127	[1]
Fuel Derivatives 2013 Maturity March 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-03	[1]
Barrels	2,112,000	[1]
Weighted-Average Floor Price	100	[1]
Weighted-Average Ceiling Price	130	[1]
Fuel Derivatives 2013 Maturity
Derivative [Line Items]
Barrels	4,224,000	[1]
Percent of Estimated Fuel Consumption	40.00%	[1]
Fuel Derivatives 2014 Maturity November 2011 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2011-11	[1]
Barrels	2,112,000	[1]
Weighted-Average Floor Price	85	[1]
Weighted-Average Ceiling Price	114	[1]
Fuel Derivatives 2014 Maturity February 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-02	[1]
Barrels	2,112,000	[1]
Weighted-Average Floor Price	88	[1]
Weighted-Average Ceiling Price	125	[1]
Fuel Derivatives 2014 Maturity June 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-06	[1]
Barrels	2,376,000	[1]
Weighted-Average Floor Price	71	[1]
Weighted-Average Ceiling Price	116	[1]
Fuel Derivatives 2014 Maturity May 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-05	[1]
Barrels	1,728,000	[1]
Weighted-Average Floor Price	85	[1]
Weighted-Average Ceiling Price	108	[1]
Fuel Derivatives 2014 Maturity
Derivative [Line Items]
Barrels	8,328,000	[1]
Percent of Estimated Fuel Consumption	39.00%	[1]
Fuel Derivatives 2015 Maturity November 2011 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2011-11	[1]
Barrels	2,160,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	114	[1]
Fuel Derivatives 2015 Maturity February 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-02	[1]
Barrels	2,160,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	125	[1]
Fuel Derivatives 2015 Maturity June 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-06	[1]
Barrels	1,236,000	[1]
Weighted-Average Floor Price	74	[1]
Weighted-Average Ceiling Price	110	[1]
Fuel Derivatives 2015 Maturity April 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-04	[1]
Barrels	1,044,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	111	[1]
Fuel Derivatives 2015 Maturity May 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-05	[1]
Barrels	1,884,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	110	[1]
Fuel Derivatives 2015 Maturity
Derivative [Line Items]
Barrels	8,484,000	[1]
Percent of Estimated Fuel Consumption	39.00%	[1]
Fuel Derivatives 2016 Maturity June 2012 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2012-06	[1]
Barrels	3,564,000	[1]
Weighted-Average Floor Price	75	[1]
Weighted-Average Ceiling Price	108	[1]
Fuel Derivatives 2016 Maturity February 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-02	[1]
Barrels	2,160,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	120	[1]
Fuel Derivatives 2016 Maturity April 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-04	[1]
Barrels	3,000,000	[1]
Weighted-Average Floor Price	75	[1]
Weighted-Average Ceiling Price	115	[1]
Fuel Derivatives 2016 Maturity
Derivative [Line Items]
Barrels	8,724,000	[1]
Percent of Estimated Fuel Consumption	40.00%	[1]
Fuel Derivatives 2017 Maturity February 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-02	[1]
Barrels	3,276,000	[1]
Weighted-Average Floor Price	80	[1]
Weighted-Average Ceiling Price	115	[1]
Fuel Derivatives 2017 Maturity April 2013 Transaction Date
Derivative [Line Items]
Derivative Inception Month And Year	2013-04	[1]
Barrels	2,028,000	[1]
Weighted-Average Floor Price	75	[1]
Weighted-Average Ceiling Price	110	[1]
Fuel Derivatives 2017 Maturity
Derivative [Line Items]
Barrels	5,304,000	[1]
Percent of Estimated Fuel Consumption	25.00%	[1]

[1] Fuel derivatives mature evenly over each month within the above fiscal periods.