Hedging - Deferred Net Gains (Losses) in AOCI Expected to Be Reclassed into Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred, Year One	$ 17,370
Cash flow hedging instruments | Currency Hedge Portfolio
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred, Year One	24,660
Cash flow hedging instruments | Bunker Fuel Forward Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred, Year One	$ (7,290)