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ASSET RETIREMENT OBLIGATION: (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Y
unit
Mar. 31, 2011
ASSET RETIREMENT OBLIGATION:    
Annual Guarantees $ 2.6  
Period of annual installments (in years) 34  
Accepted value of the Lima office building 17  
Number of units with future closure costs recognized as an asset retirement obligation 3  
Asset retirement obligation activity    
Balance at the beginning of the period 62.0 59.1
Accretion expense 0.8 0.8
Balance at the end of the period $ 62.8 $ 59.9