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Convertible Debentures and Credit Arrangements - Convertible Senior Debentures due 2024 - Additional Information (Detail) (Convertible Senior Debentures due 2024, USD $)
In Millions, except Per Share data, unless otherwise specified
6 Months Ended
Jun. 30, 2013
Dec. 31, 2004
Debt Instrument [Line Items]    
Convertible senior debentures, convertible latest date Mar. 14, 2024  
Conversion price (in dollars per share) $ 43.3044  
Fair value of Debentures outstanding $ 0.4  
Aggregate face value of convertible senior debentures   $ 150.0
Credit facility maturity date Mar. 15, 2024  
Convertible senior debentures, interest payment description Semi-annually  
Percentage of face amount which is equal to repurchase price for providing optional conversion of debentures 100.00%  
Description of conversion for convertible senior debentures The remaining 2024 Debenture holders have the right to require the Company to repurchase the 2024 Debentures on March 20, 2014 or March 20, 2019 at a repurchase price equal to 100% of their face amount, plus accrued and unpaid interest. In limited circumstances, the Company has the right to redeem all or some of the 2024 Debentures.  
Scenario 1
   
Debt Instrument [Line Items]    
Convertible senior debentures, optional repurchase date Mar. 20, 2014  
Scenario 2
   
Debt Instrument [Line Items]    
Convertible senior debentures, optional repurchase date Mar. 20, 2019