Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair value of assets and liabilities measured on recurring basis
Short-term investments	$ 122,249	$ 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	122,249	133,848
Total	122,249	133,848
Fair value measurements recurring basis | Significant Observable Inputs (Level 2)
Fair value of assets and liabilities measured on recurring basis
Forward contracts	1,579	5,105
Total	1,579	5,105
Fair value measurements recurring basis | Total
Fair value of assets and liabilities measured on recurring basis
Short-term investments	122,249	133,848
Forward contracts	1,579	5,105
Total	$ 123,828	$ 138,953