Fair Value Measurements (Details) (Recurring basis, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Total
Assets measured at fair value
Cash equivalents	$ 303,816	$ 304,159
Restricted cash	21,000
Total assets measured at fair value	336,846	317,253
Liabilities measured at fair value
Total liabilities measured at fair value	16,276	397
Total | Fuel derivative contracts
Assets measured at fair value
Derivative contracts	6,717	13,094
Liabilities measured at fair value
Derivative contracts	736	397
Total | Foreign currency derivatives
Assets measured at fair value
Derivative contracts	4,856
Liabilities measured at fair value
Derivative contracts	2,675
Total | Interest rate derivatives
Assets measured at fair value
Derivative contracts	457
Total | Negative arbitrage derivative
Liabilities measured at fair value
Derivative contracts	12,865
Level 1
Assets measured at fair value
Cash equivalents	303,816	304,159
Restricted cash	21,000
Total assets measured at fair value	324,816	304,159
Level 2
Assets measured at fair value
Total assets measured at fair value	12,030	13,094
Liabilities measured at fair value
Total liabilities measured at fair value	3,411	397
Level 2 | Fuel derivative contracts
Assets measured at fair value
Derivative contracts	6,717	13,094
Liabilities measured at fair value
Derivative contracts	736	397
Level 2 | Foreign currency derivatives
Assets measured at fair value
Derivative contracts	4,856
Liabilities measured at fair value
Derivative contracts	2,675
Level 2 | Interest rate derivatives
Assets measured at fair value
Derivative contracts	457
Level 3
Liabilities measured at fair value
Total liabilities measured at fair value	12,865
Level 3 | Negative arbitrage derivative
Liabilities measured at fair value
Derivative contracts	$ 12,865