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Commitment and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended 1 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Aug. 31, 2013
Senior Convertible Notes
Sep. 30, 2013
Senior Convertible Notes
Debt Instrument [Line Items]            
Proceeds from Issuance of Debt         $ 150  
Interest rate           1.50%
Operating lease payment of non-cancelable agreement expiration period     through September 30, 2022      
Rent expense $ 2.0 $ 2.1 $ 6.4 $ 6.4