FAIR VALUE MEASUREMENTS (Policy)	3 Months Ended
Jun. 30, 2012
Notes to Financial Statements [Abstract]
Fair Value of Financial Instruments, Policy	10. FAIR VALUE MEASUREMENTS Accounting standards pertaining to fair value measurements establish a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. As of June 30, 2012, the Company held certain items that are required to be measured at fair value on a recurring basis. These included cash equivalents, short-term investments (primarily treasury bills, commercial paper, and certificates of deposit), certain noncurrent investments, interest rate derivative contracts, fuel derivative contracts, and available-for-sale securities. The majority of the Company's short-term investments consist of instruments classified as Level 1. However, the Company has certificates of deposit and commercial paper that are classified as Level 2, due to the fact that the fair value for these instruments is determined utilizing observable inputs in non-active markets. Noncurrent investments consist of certain auction rate securities, primarily those collateralized by student loan portfolios, which are guaranteed by the U.S. Government. Other available-for-sale securities primarily consist of investments associated with the Company's excess benefit plan. The Company's fuel and interest rate derivative instruments consist of over-the-counter (OTC) contracts, which are not traded on a public exchange. Fuel derivative instruments include swaps, as well as different types of option contracts, whereas interest rate derivatives consist solely of swap agreements. See Note 5 for further information on the Company's derivative instruments and hedging activities. The fair values of swap contracts are determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets. Therefore, the Company has categorized these swap contracts as Level 2. The Company's Treasury Group, which reports to the Chief Financial Officer, determines the value of option contracts utilizing an option pricing model based on inputs that are either readily available in public markets, can be derived from information available in publicly quoted markets, or are provided by financial institutions that trade these contracts. The option pricing model used by the Company is an industry standard model for valuing options and is the same model used by the broker/dealer community (i.e., the Company's counterparties). The inputs to this option pricing model are the option strike price, underlying price, risk free rate of interest, time to expiration, and volatility. Because certain inputs used to determine the fair value of option contracts are unobservable (principally implied volatility), the Company has categorized these option contracts as Level 3. Volatility information is obtained from external sources, but is analyzed by the Company for reasonableness and compared to similar information received from other external sources. The fair value of option contracts considers both the intrinsic value and any remaining time value associated with those derivatives that have not yet settled. The Company also considers counterparty credit risk and its own credit risk in its determination of all estimated fair values. To validate the reasonableness of the Company's option pricing model, on a monthly basis, the Company compares its option valuations to third party valuations. If any significant differences were to be noted, they would be researched in order to determine the reason. However, historically, no significant differences have been noted. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds. All settlements from fuel derivative contracts that are deemed “effective” are included in Fuel and oil expense in the period the underlying fuel is consumed in operations. Any “ineffectiveness” associated with hedges, including amounts that settled in the current period (realized), and amounts that will settle in future periods (unrealized), is recorded in earnings immediately, as a component of Other (gains) losses, net. See Note 5 for further information on hedging. Any gains and losses (realized and unrealized) related to other investments are reported in Other operating expenses, and were immaterial for the three and six months ended June 30, 2012 and 2011.

FAIR VALUE MEASUREMENTS (Policy)

3 Months Ended

Jun. 30, 2012

Notes to Financial Statements [Abstract]

Fair Value of Financial Instruments, Policy

10. FAIR VALUE MEASUREMENTS

Accounting standards pertaining to fair value measurements establish a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.

As of June 30, 2012, the Company held certain items that are required to be measured at fair value on a recurring basis. These included cash equivalents, short-term investments (primarily treasury bills, commercial paper, and certificates of deposit), certain noncurrent investments, interest rate derivative contracts, fuel derivative contracts, and available-for-sale securities. The majority of the Company's short-term investments consist of instruments classified as Level 1. However, the Company has certificates of deposit and commercial paper that are classified as Level 2, due to the fact that the fair value for these instruments is determined utilizing observable inputs in non-active markets. Noncurrent investments consist of certain auction rate securities, primarily those collateralized by student loan portfolios, which are guaranteed by the U.S. Government. Other available-for-sale securities primarily consist of investments associated with the Company's excess benefit plan.

The Company's fuel and interest rate derivative instruments consist of over-the-counter (OTC) contracts, which are not traded on a public exchange. Fuel derivative instruments include swaps, as well as different types of option contracts, whereas interest rate derivatives consist solely of swap agreements. See Note 5 for further information on the Company's derivative instruments and hedging activities. The fair values of swap contracts are determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets. Therefore, the Company has categorized these swap contracts as Level 2. The Company's Treasury Group, which reports to the Chief Financial Officer, determines the value of option contracts utilizing an option pricing model based on inputs that are either readily available in public markets, can be derived from information available in publicly quoted markets, or are provided by financial institutions that trade these contracts. The option pricing model used by the Company is an industry standard model for valuing options and is the same model used by the broker/dealer community (i.e., the Company's counterparties). The inputs to this option pricing model are the option strike price, underlying price, risk free rate of interest, time to expiration, and volatility. Because certain inputs used to determine the fair value of option contracts are unobservable (principally implied volatility), the Company has categorized these option contracts as Level 3. Volatility information is obtained from external sources, but is analyzed by the Company for reasonableness and compared to similar information received from other external sources. The fair value of option contracts considers both the intrinsic value and any remaining time value associated with those derivatives that have not yet settled. The Company also considers counterparty credit risk and its own credit risk in its determination of all estimated fair values. To validate the reasonableness of the Company's option pricing model, on a monthly basis, the Company compares its option valuations to third party valuations. If any significant differences were to be noted, they would be researched in order to determine the reason. However, historically, no significant differences have been noted. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds.

All settlements from fuel derivative contracts that are deemed “effective” are included in Fuel and oil expense in the period the underlying fuel is consumed in operations. Any “ineffectiveness” associated with hedges, including amounts that settled in the current period (realized), and amounts that will settle in future periods (unrealized), is recorded in earnings immediately, as a component of Other (gains) losses, net. See Note 5 for further information on hedging. Any gains and losses (realized and unrealized) related to other investments are reported in Other operating expenses, and were immaterial for the three and six months ended June 30, 2012 and 2011.