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ASSET RETIREMENT OBLIGATION: (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Y
unit
Jun. 30, 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 1.7 1.7
Balance at the end of the period $ 63.7 $ 60.8