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, USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives Not Designated as Hedging Instruments | Commodity contracts | Fuel price derivatives, at fair value
Derivatives, Fair Value [Line Items]
Derivatives Classified as Assets	$ 0	$ 0
Derivatives Classified as Liabilities	$ 4,535	$ 7,358