Derivative Instruments (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Derivative Instruments
Contract period of foreign currency forward contracts	3 months	3 months

Maximum amount of time remaining before foreign currency exchange rate derivatives mature or expire, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_MaximumRemainingMaturityOfForeignCurrencyDerivatives1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration