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Fair Value Measurements (Tables)
6 Months Ended
Jun. 30, 2012
Fair Value Disclosures [Abstract]  
Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis
 
Estimated Fair Value at
December 31, 2011
 
Level 1
 
Level 2
 
Level 3
Corporate bonds (Note 4)
$
25,709

 
$

 
$
25,709

 
$

Cash equivalents
$
159,719

 
$
159,719

 
$

 
$

 
Estimated Fair Value at
June 30, 2012
 
Level 1
 
Level 2
 
Level 3
Corporate bonds (Note 4)
$
19,459

 
$

 
$
19,459

 
$

Cash equivalents
$
245,389

 
$
245,389

 
$

 
$