Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012
Assets (Liabilties) at Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	$ (6,067)		$ (13,005)		$ 4,273
Assets (Liabilties) at Fair Value | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	1,488		1,636		5,508
Available-for-sale investment			1,668
Assets (Liabilties) at Fair Value | Other current assets | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	2,974	[1]	192	[1]	2,091	[1]
Gross amounts offset in the balance sheets	(2,227)	[1]	(2,550)	[1]	(2,871)	[1]
Assets (Liabilties) at Fair Value | Other current assets | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	569		4,001		6,825
Gross amounts offset in the balance sheets	(34)
Assets (Liabilties) at Fair Value | Other current assets | Not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	206		4
Gross amounts offset in the balance sheets			(11)		(537)
Assets (Liabilties) at Fair Value | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	137		830		74
Available-for-sale investment					4,161
Assets (Liabilties) at Fair Value | Investments & other assets, net | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	137	[1]			200	[1]
Gross amounts offset in the balance sheets					(265)	[1]
Assets (Liabilties) at Fair Value | Investments & other assets, net | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets			1,889		852
Gross amounts offset in the balance sheets			(1,059)		(713)
Assets (Liabilties) at Fair Value | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(4,549)		(17,139)		(972)
Assets (Liabilties) at Fair Value | Accrued liabilities | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	1,194	[1]	1,992	[1]	2,622	[1]
Gross amounts of recognized liabilities	(5,638)	[1]	(22,849)	[1]	(3,328)	[1]
Assets (Liabilties) at Fair Value | Accrued liabilities | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	1,531		3,741		880
Gross amounts of recognized liabilities	(1,005)
Assets (Liabilties) at Fair Value | Accrued liabilities | Not designated as hedging instruments | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	25	[2]
Gross amounts of recognized liabilities	(883)	[2]
Assets (Liabilties) at Fair Value | Accrued liabilities | Not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	227		1
Gross amounts of recognized liabilities			(24)		(1,146)
Assets (Liabilties) at Fair Value | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(3,143)				(4,498)
Assets (Liabilties) at Fair Value | Other liabilities | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	221	[1]			4,000	[1]
Gross amounts of recognized liabilities	(100)	[1]			(4,976)	[1]
Assets (Liabilties) at Fair Value | Other liabilities | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	43				654
Gross amounts of recognized liabilities	(3,307)				(4,176)
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value			1,668		4,161
Level 1 | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale investment			1,668
Level 1 | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale investment					4,161
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	(6,067)		(14,673)		112
Level 2 | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	1,488		1,636		5,508
Level 2 | Other current assets | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	2,974	[1]	192	[1]	2,091	[1]
Gross amounts offset in the balance sheets	(2,227)	[1]	(2,550)	[1]	(2,871)	[1]
Level 2 | Other current assets | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	569		4,001		6,825
Gross amounts offset in the balance sheets	(34)
Level 2 | Other current assets | Not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	206		4
Gross amounts offset in the balance sheets			(11)		(537)
Level 2 | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	137		830		74
Level 2 | Investments & other assets, net | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	137	[1]			200	[1]
Gross amounts offset in the balance sheets					(265)	[1]
Level 2 | Investments & other assets, net | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets			1,889		852
Gross amounts offset in the balance sheets			(1,059)		(713)
Level 2 | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(4,549)		(17,139)		(972)
Level 2 | Accrued liabilities | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	1,194	[1]	1,992	[1]	2,622	[1]
Gross amounts of recognized liabilities	(5,638)	[1]	(22,849)	[1]	(3,328)	[1]
Level 2 | Accrued liabilities | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	1,531		3,741		880
Gross amounts of recognized liabilities	(1,005)
Level 2 | Accrued liabilities | Not designated as hedging instruments | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	25	[2]
Gross amounts of recognized liabilities	(883)	[2]
Level 2 | Accrued liabilities | Not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	227		1
Gross amounts of recognized liabilities			(24)		(1,146)
Level 2 | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(3,143)				(4,498)
Level 2 | Other liabilities | Designated as cash flow hedges | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	221	[1]			4,000	[1]
Gross amounts of recognized liabilities	(100)	[1]			(4,976)	[1]
Level 2 | Other liabilities | Designated as cash flow hedges | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	43				654
Gross amounts of recognized liabilities	$ (3,307)				$ (4,176)

[1] Currency hedge portfolio positions designated as cash flow hedges.

[2] Currency hedge portfolio positions not designated as hedging instruments.