Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Assets (Liabilties) at Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	$ 96		$ (3,781)		$ (6,067)
Assets (Liabilties) at Fair Value | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	820				1,488
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	1,259	[1]			2,974	[1]
Gross amounts offset in the balance sheets	(1,171)	[1]			(2,227)	[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	830				569
Gross amounts offset in the balance sheets	(14)				(34)
Assets (Liabilties) at Fair Value | Other current assets | 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 assets					206
Gross amounts offset in the balance sheets	(84)
Assets (Liabilties) at Fair Value | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	293		633		137
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
Gross amounts offset in the balance sheets			(220)	[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	293		953
Gross amounts offset in the balance sheets			(100)
Assets (Liabilties) at Fair Value | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(1,007)		(4,317)		(4,549)
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	2,482	[1]	1,250	[1]	1,194	[1]
Gross amounts of recognized liabilities	(3,081)	[1]	(5,947)	[1]	(5,638)	[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	322		778		1,531
Gross amounts of recognized liabilities	(476)		(643)		(1,005)
Assets (Liabilties) at Fair Value | Accrued liabilities | Derivatives 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 | 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		227
Gross amounts of recognized liabilities	(254)
Assets (Liabilties) at Fair Value | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(10)		(97)		(3,143)
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	[1]	221	[1]
Gross amounts of recognized liabilities			(930)	[1]	(100)	[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
Gross amounts of recognized liabilities	(10)				(3,307)
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets (liabilities) at fair value	96		(3,781)		(6,067)
Level 2 | Other current assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	820				1,488
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	1,259	[1]			2,974	[1]
Gross amounts offset in the balance sheets	(1,171)	[1]			(2,227)	[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	830				569
Gross amounts offset in the balance sheets	(14)				(34)
Level 2 | Other current assets | 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 assets					206
Gross amounts offset in the balance sheets	(84)
Level 2 | Investments & other assets, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded assets	293		633		137
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
Gross amounts offset in the balance sheets			(220)	[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	293		953
Gross amounts offset in the balance sheets			(100)
Level 2 | Accrued liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(1,007)		(4,317)		(4,549)
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	2,482	[1]	1,250	[1]	1,194	[1]
Gross amounts of recognized liabilities	(3,081)	[1]	(5,947)	[1]	(5,638)	[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	322		778		1,531
Gross amounts of recognized liabilities	(476)		(643)		(1,005)
Level 2 | Accrued liabilities | Derivatives 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 | 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		227
Gross amounts of recognized liabilities	(254)
Level 2 | Other liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net amount of recorded liabilities	(10)		(97)		(3,143)
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	[1]	221	[1]
Gross amounts of recognized liabilities			(930)	[1]	(100)	[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
Gross amounts of recognized liabilities	$ (10)				$ (3,307)

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

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