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Schedule Of Additional Information About Investments In An Unrealized Loss Position (Detail)
Jun. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Number of issues (Cusip numbers) held, Less than Twelve Months 87 117
Number of issues (Cusip numbers) held, Twelve Months or Longer 96 93
Number of issues (Cusip numbers) held, Total 183 210