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Comprehensive Income
6 Months Ended
Jun. 30, 2011
Comprehensive Income [Abstract]  
COMPREHENSIVE INCOME
6. COMPREHENSIVE INCOME.
     Comprehensive income is as follows:
                                 
    Three months ended     Six months ended  
    June 30,     June 30,  
    2011     2010     2011     2010  
            (Thousands of Dollars)          
Net income
  $ 35,379     $ 34,378     $ 75,062     $ 72,261  
Amortization of cash flow hedges
    (16 )     (16 )     (31 )     (31 )
 
                       
Total comprehensive income
  $ 35,363     $ 34,362     $ 75,031     $ 72,230