Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair value of assets and liabilities measured on recurring basis
Short-term investments	$ 167,345	$ 133,848
Fair value measurements recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value of assets and liabilities measured on recurring basis
Short-term investments	167,345	133,848
Total	167,345	133,848
Fair value measurements recurring basis | Significant Observable Inputs (Level 2)
Fair value of assets and liabilities measured on recurring basis
Forward contracts	7,062	5,105
Total	7,062	5,105
Fair value measurements recurring basis | Total
Fair value of assets and liabilities measured on recurring basis
Short-term investments	167,345	133,848
Forward contracts	7,062	5,105
Total	$ 174,407	$ 138,953