Hedging Derivative Assets and Liabilities Table (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011
Foreign currency derivatives [Member]
Derivatives, Fair Value [Line Items]
Balance at beginning of period	$ (2,527)		$ 0		$ 5,232		$ 387		$ 4,204		$ 293
Realized (gains) losses included in net income	1,018		(53)		(4,381)		445		1,386		1,586
Purchases (sales), net	0	[1]	850	[1]	0	[1]	0	[1]	0	[1]	5,013	[1]
Changes in fair value	(14,109)		(3,324)		(851)		6,000		(5,203)		(2,688)
Balance at end of period	(15,618)		(2,527)		0		6,832		387		4,204
Bunker fuel forward contracts [Member]
Derivatives, Fair Value [Line Items]
Balance at beginning of period	4,322		28,711		14,754		53,990		59,824		27,314
Realized (gains) losses included in net income	(3,822)		(4,139)		(5,514)		(10,475)		(12,240)		(5,428)
Purchases (sales), net	0	[1]	0	[1]	0	[1]	(3,288)	[1]	0	[1]	0	[1]
Changes in fair value	12,551		(20,250)		19,471		(18,933)		6,406		37,938
Balance at end of period	$ 13,051		$ 4,322		$ 28,711		$ 21,294		$ 53,990		$ 59,824

[1] Purchases (sales) represent the cash premiums paid upon the purchase of euro put options or received upon the sale of euro call options and sales of bunker fuel forward contracts prior to their expiration. Bunker fuel forward contracts require no up-front cash payment and have an initial fair value of zero; settlements on the forward contracts (swaps) occur upon the maturity of the forward contracts