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Subsequent Event - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 1 Months Ended 1 Months Ended
Dec. 31, 2009
Jan. 31, 2012
Financing
3.5% exchangeable senior notes due 2032
Jan. 09, 2012
Financing
3.5% exchangeable senior notes due 2032
Jan. 31, 2012
Private Placement
3.5% exchangeable senior notes due 2032
Jan. 09, 2012
Private Placement
3.5% exchangeable senior notes due 2032
Jan. 31, 2012
Private Placement
3.5% exchangeable senior notes due 2032
Minimum
Jan. 31, 2012
Private Placement
3.5% exchangeable senior notes due 2032
Maximum
Subsequent Event [Line Items]              
Convertible senior notes     $ 150,000,000        
Convertible senior notes, stated interest rate     3.50%        
Proceeds from private placement of convertible senior notes $ 5,600,000 $ 144,300,000          
Convertible senior notes, payment start date   2012-07-15          
Convertible senior notes, maturity date   Jan. 15, 2032          
Percentage of repurchase price to principal amount     100.00%        
Convertible senior notes, conversion starting date       Oct. 15, 2031      
Convertible senior notes, number of shares of common stock per $1,000 principal amount of notes         113.4572    
Convertible senior notes, conversion price per share of common stock       $ 8.8125      
Convertible senior notes, conversion circumstance, last reported sale price of common stock as percentage of conversion price           130.00%  
Convertible senior notes, conversion circumstance, trading price per $1,000 principal amount of notes as percentage of the product of the last reported sale price             98.00%