Location and Amounts of Derivative Fair Values in Condensed Consolidated Balance Sheets (Detail) (Derivatives Not Designated as Hedging Instruments, Commodity contracts, Fuel Price Derivatives At Fair Value [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives Not Designated as Hedging Instruments | Commodity contracts | Fuel Price Derivatives At Fair Value [Member]
Derivatives, Fair Value [Line Items]
Derivatives Classified as Assets	$ 6,782	$ 0
Derivatives Classified as Liabilities	$ 0	$ 7,358