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INDEBTEDNESS (NARRATIVE) (DETAILS) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Mar. 31, 2012
INDEBTEDNESS [ABSTRACT]      
Increase in borrowing capacity     $ 150,000,000
Maximum borrowing capacity     500,000,000
Borrowings outstanding on credit facility 108,000,000 64,000,000  
Average daily utilization under credit facility 154,500,000 112,400,000  
Letters of credit issued under credit facility 3,800,000    
Remaining borrowing capacity under credit facility $ 388,200,000