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Changes in Fair value of Level 3 Financial Assets (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Derivative [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance $ 2.6 $ 1.7
Additions   0.4
Unrealized (loss)/ gain (1.3) 0.5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance $ 1.3 $ 2.6