Cash, Cash Equivalents, and Short-Term Investments (Details 1) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Summary of cost and estimated fair value of short-term investments    
Amortized Cost of short-term investments, Due within one year $ 27,470  
Amortized Cost of short-term investments, Due within two years 12,955  
Short-term investments, Amortized Cost 40,425  
Estimated fair value of short-term investments, Due within one year 27,446  
Estimated fair value of short-term investments, Due within two years 12,961  
Short-term investments, Estimated Fair Value $ 40,407 $ 1,587 [1]
[1] The Condensed Consolidated Balance Sheet as of December 31, 2011 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.