Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value			$ 0
Investments & other assets, net | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	(1,936)	[1]
Assets (Liabilties) at Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	(4,627)		(3,781)		3,038
Assets (Liabilties) at Fair Value | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets					3,103
Assets (Liabilties) at Fair Value | Other current assets | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					5,219
Assets (Liabilties) at Fair Value | Other current assets | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					(186)
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					2,078	[1]
Gross amounts offset in the balance sheets					(2,935)	[1]
Assets (Liabilties) at Fair Value | Other current assets | Derivatives not designated as hedging instruments | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					187	[2]
Gross amounts offset in the balance sheets					(1,260)	[2]
Assets (Liabilties) at Fair Value | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	417		633		3,250
Assets (Liabilties) at Fair Value | Investments & other assets, net | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	2,146	[1]
Gross amounts offset in the balance sheets	(1,936)	[1]
Assets (Liabilties) at Fair Value | Investments & other assets, net | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	373		953
Gross amounts offset in the balance sheets	(166)		(100)
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					3,024	[1]
Gross amounts offset in the balance sheets					(632)	[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					1,679
Gross amounts offset in the balance sheets					(821)
Assets (Liabilties) at Fair Value | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(5,044)		(4,317)		(3,315)
Assets (Liabilties) at Fair Value | Accrued liabilities | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	2,937	[1]	1,250	[1]
Gross amounts of recognized liabilities	(6,978)	[1]	(5,947)	[1]
Assets (Liabilties) at Fair Value | Accrued liabilities | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			643
Gross amounts offset in the balance sheets	317		778
Gross amounts of recognized liabilities	(1,158)
Assets (Liabilties) at Fair Value | Accrued liabilities | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			245
Gross amounts of recognized liabilities	(162)
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					1,456	[1]
Gross amounts of recognized liabilities					(6,116)	[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					1,544
Assets (Liabilties) at Fair Value | Accrued liabilities | Derivatives not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized liabilities					(199)
Assets (Liabilties) at Fair Value | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets and liabilities at fair value			(97)
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	(4,627)		(3,781)		3,038
Level 2 | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets					3,103
Level 2 | Other current assets | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					5,219
Level 2 | Other current assets | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					(186)
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					2,078	[1]
Gross amounts offset in the balance sheets					(2,935)	[1]
Level 2 | Other current assets | Derivatives not designated as hedging instruments | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					187	[2]
Gross amounts offset in the balance sheets					(1,260)	[2]
Level 2 | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	417		633		3,250
Level 2 | Investments & other assets, net | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	2,146	[1]
Level 2 | Investments & other assets, net | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	373		953
Gross amounts offset in the balance sheets	(166)		(100)
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					3,024	[1]
Gross amounts offset in the balance sheets					(632)	[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					1,679
Gross amounts offset in the balance sheets					(821)
Level 2 | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(5,044)		(4,317)		(3,315)
Level 2 | Accrued liabilities | Currency hedge portfolio
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	2,937	[1]	1,250	[1]
Gross amounts of recognized liabilities	(6,978)	[1]	(5,947)	[1]
Level 2 | Accrued liabilities | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets	317		778
Gross amounts of recognized liabilities	(1,158)		643
Level 2 | Accrued liabilities | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			245
Gross amounts of recognized liabilities	(162)
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					1,456	[1]
Gross amounts of recognized liabilities					(6,116)	[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					1,544
Level 2 | Accrued liabilities | Derivatives not designated as hedging instruments | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized liabilities					(199)
Level 2 | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets and liabilities at fair value			(97)
Currency hedge portfolio [Member] | Assets (Liabilties) at Fair Value | Gross liabilties included in Other liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized liabilities			(930)	[1]
Currency hedge portfolio [Member] | Assets (Liabilties) at Fair Value | Gross Liabilities Included in Investments & other assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			(220)	[1]
Currency hedge portfolio [Member] | Assets (Liabilties) at Fair Value | Gross Assets Included in Other Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			833	[1]
Currency hedge portfolio [Member] | Level 2 | Gross liabilties included in Other liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized liabilities			(930)	[1]
Currency hedge portfolio [Member] | Level 2 | Gross Liabilities Included in Investments & other assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			(220)	[1]
Currency hedge portfolio [Member] | Level 2 | Gross Assets Included in Other Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets			$ 833	[1]

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