Derivative financial instruments Summary of information about the fair values of derivative instruments on consolidated balance sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	$ 14,823	$ 100,475
Derivative Liability, Fair Value, Gross Liability	65,248	5,710
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	14,698	100,235
Derivative Liability, Fair Value, Gross Liability	65,227	5,672
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	125	240
Derivative Liability, Fair Value, Gross Liability	21	38
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	14,556	77,066
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	54,597	5,052
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	142	23,169
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Obligations [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	10,630	620
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset Fair Value [Abstract]	125	240
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 21	$ 38