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Receivables (Tables)
3 Months Ended
Mar. 31, 2012
Receivables [Abstract]  
Receivables
The components of receivables were as follows (in thousands):

   
March 31,
  
December 31,
 
   
2012
  
2011
 
Billed
 $59,330  $77,505 
Unbilled
  361,020   255,962 
Total
 $420,350  $333,467