Hedging Derivative Assets and Liabilities Table (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Foreign currency derivatives [Member]
Derivatives, Fair Value [Line Items]
Balance at beginning of period	$ (23,215)		$ 5,232
Realized (gains) losses included in net income	8,722		(4,381)
Derivative Instruments Not Designated as Hedging Instruments, Type	7638
Purchases (sales), net	541	[1]	0	[1]
Changes in fair value	3,189		(851)
Balance at end of period	(3,125)		0
Bunker fuel forward contracts [Member]
Derivatives, Fair Value [Line Items]
Balance at beginning of period	8,572		14,754
Realized (gains) losses included in net income	(2,839)		(5,514)
Purchases (sales), net	0	[1]	0	[1]
Changes in fair value	1,888		19,471
Balance at end of period	$ 7,621		$ 28,711

[1] Bunker fuel and currency forward contracts require no up-front cash payment and have an initial fair value of zero; settlements on the forward contracts (swaps) occur upon their maturity