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Summary of Significant Accounting Policies (Cash and Cash Equivalents and Short Term Investment) - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2012
Cash and cash equivalents | Maximum
  
Summary Of Significant Accounting Policies [Line Items]  
Maturity period used to classify investments 3 months
Short-term Investments
  
Summary Of Significant Accounting Policies [Line Items]  
Period which investments to be reclassified to short term investment from long term investment 12 months
Short-term Investments | Maximum
  
Summary Of Significant Accounting Policies [Line Items]  
Maturity period used to classify investments 12 months
Short-term Investments | Minimum
  
Summary Of Significant Accounting Policies [Line Items]  
Maturity period used to classify investments 3 months