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Basis of Presentation - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]        
Research and development expenses $ 14.3 $ 13.9 $ 28.7 $ 26.5