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ASSET RETIREMENT OBLIGATION: (Details) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Sep. 30, 2013
item
Sep. 30, 2012
ASSET RETIREMENT OBLIGATION:    
Accepted value of the Lima office building $ 17  
Cumulative guarantee amount 10.5  
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 118.2 62.0
Closure payments (0.7)  
Accretion expense 7.4 2.6
Balance at the end of the period $ 124.9 $ 64.6