Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Assets (Liabilties) at Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	$ 18,972		$ (3,781)		$ (10,051)
Assets (Liabilties) at Fair Value | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	18,972
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	22,593
Gross amounts offset in the balance sheets	(750)
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 offset in the balance sheets	(3,373)	[1]
Assets (Liabilties) at Fair Value | Other current assets | Designated as cash flow hedges | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	502
Assets (Liabilties) at Fair Value | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets			633		61
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					515
Gross amounts offset in the balance sheets			(220)		(465)
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			953	[1]	196
Gross amounts offset in the balance sheets			(100)	[1]	(137)
Assets (Liabilties) at Fair Value | Investments & other assets, net | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					22
Gross amounts offset in the balance sheets					(70)
Assets (Liabilties) at Fair Value | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities			(4,317)		(9,161)
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			1,250		1,163
Gross amounts of recognized liabilities			(5,947)		(10,913)
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			778	[1]	1,212	[1]
Gross amounts of recognized liabilities			(643)	[1]	(611)	[1]
Assets (Liabilties) at Fair Value | Accrued liabilities | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					282	[2]
Gross amounts of recognized liabilities					(203)	[2]
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 offset in the balance sheets			245		17
Gross amounts of recognized liabilities					(108)
Assets (Liabilties) at Fair Value | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities			(97)		(951)
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			833		196
Gross amounts of recognized liabilities			(930)		(233)
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					145	[1]
Gross amounts of recognized liabilities					(835)	[1]
Assets (Liabilties) at Fair Value | Other liabilities | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					12	[2]
Gross amounts of recognized liabilities					(236)	[2]
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	18,972		(3,781)		(10,051)
Level 2 | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	18,972
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	22,593
Gross amounts offset in the balance sheets	(750)
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 offset in the balance sheets	(3,373)	[1]
Level 2 | Other current assets | Designated as cash flow hedges | 30-day euro forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets	502
Level 2 | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets			633		61
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					515
Gross amounts offset in the balance sheets			(220)		(465)
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			953	[1]	196
Gross amounts offset in the balance sheets			(100)	[1]	(137)
Level 2 | Investments & other assets, net | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts of recognized assets					22
Gross amounts offset in the balance sheets					(70)
Level 2 | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities			(4,317)		(9,161)
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			1,250		1,163
Gross amounts of recognized liabilities			(5,947)		(10,913)
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			778	[1]	1,212	[1]
Gross amounts of recognized liabilities			(643)	[1]	(611)	[1]
Level 2 | Accrued liabilities | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					282	[2]
Gross amounts of recognized liabilities					(203)	[2]
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 offset in the balance sheets			245		17
Gross amounts of recognized liabilities					(108)
Level 2 | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities			(97)		(951)
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			833		196
Gross amounts of recognized liabilities			(930)		(233)
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					145	[1]
Gross amounts of recognized liabilities					(835)	[1]
Level 2 | Other liabilities | Derivatives not designated as hedging instruments | Bunker fuel forward contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amounts offset in the balance sheets					12	[2]
Gross amounts of recognized liabilities					$ (236)	[2]

[1] Bunker fuel forward contracts designated as cash flow hedges.

[2] Bunker fuel forward contracts not designated as hedging instruments.