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Cash and Cash Equivalents (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2011
Dec. 31, 2010
Dec. 31, 2009
Dec. 31, 2008
Cash and Cash Equivalents            
Cash   $ 4,555   $ 429    
Investments with original maturity of less than three months at the time of purchase   19,894   29,066    
Total cash and cash equivalents $ 17,837 $ 24,449 $ 27,675 $ 29,495 $ 11,493 $ 24,220