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Stock-Based Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2010
Jun. 22, 2012
Chairman And Founder [Member]
Aug. 16, 2012
Chairman And Founder [Member]
Feb. 26, 2012
Chairman And Founder [Member]
Jul. 13, 2011
Chairman And Founder [Member]
Dec. 31, 2012
Stock option plan 2009 [Member]
Dec. 31, 2011
Stock option plan 2009 [Member]
Dec. 31, 2012
Stock option plan 1987 [Member]
Dec. 31, 2012
1987 Stock Option Plan granted prior to December 2003 [Member]
Schedule Of Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Activity [Line Items]                    
Maximum number of shares, issued under the option plan             16,000,000      
Number of shares available to be granted             8,457,666 9,770,666    
Period of granted option             7 years   7 years 10 years
Option vested under stock option plan to employees and consultants             One-third on each of the first three anniversaries of the date of grant      
Exercised number of shares, under stock option plan     1,083,333 900,001            
Cash payments made on cashless exercise of stock options     $ 25 $ 15 $ 4 $ 5        
Holding period of restricted stock available to executive 4 years                  
Share based compensation arrangement long-term retention program restricted stock available to executive releasing period 10 years                  
Number of days considered for weighted average trading price 20 days                  
Percentage of annual retainers 60.00%                  
Percentage of additional annual retainers 100.00%                  
Percentage of increments 25.00%                  
One-time compensation expense   $ 20