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Convertible Senior Notes - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 1 Months Ended 3 Months Ended 1 Months Ended 3 Months Ended 1 Months Ended
Nov. 30, 2009
Mar. 31, 2013
Jan. 03, 2012
4.50% Convertible senior notes (due 2014)
Nov. 30, 2009
4.50% Convertible senior notes (due 2014)
Mar. 31, 2013
4.50% Convertible senior notes (due 2014)
Mar. 31, 2012
4.50% Convertible senior notes (due 2014)
Dec. 31, 2012
4.50% Convertible senior notes (due 2014)
Apr. 01, 2013
4.50% Convertible senior notes (due 2014)
Subsequent Event
Nov. 30, 2009
4.50% Convertible senior notes (due 2014)
Scenario, Forecast
Debt Instrument [Line Items]                  
Long term debt, face amount       $ 100.0          
Debt instrument, interest rate       4.50%          
Frequency of interest payment       Semi-annually          
Debt instrument, maturity date   Apr. 02, 2013   Nov. 01, 2014 Nov. 01, 2014        
Conversion rate in share per $1000 principal amount of notes       63.2091         68.3831
Debt instrument, conversion rate       $ 15.82         $ 14.62
Cash dividend on common stock per share paid     $ 0.10         $ 0.07  
Debt discount 13.7                
Interest expenses associated with amortization of equity component         0.7 0.7      
Debt instrument unamortized discount         $ 4.4   $ 5.1