Derivative Instruments - Location and Amounts of Derivative Fair Values in Condensed Consolidated Balance Sheets (Detail) - Derivatives Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands |
Sep. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Commodity contracts [Member] | Fuel Price Derivatives at Fair Value [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Derivatives Classified as Assets | $ 13,417 | $ 40,969 |
| Derivatives Classified as Liabilities | 0 | 0 |
| Foreign Currency Exchange Contract [Member] | Accounts Receivable [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Derivatives Classified as Assets | 15 | 0 |
| Foreign Currency Exchange Contract [Member] | Accounts Payable [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Derivatives Classified as Liabilities | $ 115 | $ 0 |