Hedging Derivative Assets and Liabilities Table (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012		Mar. 31, 2012		Jun. 30, 2011		Mar. 31, 2011
Bunker fuel forward contracts [Member]
Derivatives, Fair Value [Line Items]
Bunker fuel forward contracts asset (liability) balance, beginning balance	$ 28,711		$ 14,754		$ 59,824		$ 27,314
Realized (gains) losses included in net income	(4,139)		(5,514)		(12,240)		(5,428)
Purchases (sales), net	0	[1]	0	[1]	0	[1]	0	[1]
Changes in fair value	(20,250)		19,471		6,406		37,938
Bunker fuel forward contracts asset (liability) balance, ending balance	4,322		28,711		53,990		59,824
Foreign currency derivatives [Member]
Derivatives, Fair Value [Line Items]
Currency hedge portfolio asset (liability) balance, beginning balance	0		5,232		4,204		293
Realized (gains) losses included in net income	(53)		(4,381)		1,386		1,586
Purchases (sales), net	850	[1]	0	[1]	0	[1]	5,013	[1]
Changes in fair value	(3,324)		(851)		(5,203)		(2,688)
Currency hedge portfolio asset (liability) balance, ending balance	$ (2,527)		$ 0		$ 387		$ 4,204

[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; instead any gain or loss on the forward contracts (swaps) is settled in cash upon the maturity of the forward contracts