Quarterly report pursuant to Section 13 or 15(d)

Stock Incentive Plan (Narrative) (Details)

v2.4.0.6
Stock Incentive Plan (Narrative) (Details) (USD $)
 3 Months Ended 9 Months Ended 9 Months Ended 26 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2010
Sep. 30, 2012
Class A Common Stock [Member]
Dec. 31, 2011
Class A Common Stock [Member]
Sep. 30, 2012
2000 Plan [Member]
Dec. 31, 2010
2000 Plan [Member]
Jun. 30, 2012
2010 Plan [Member]
Class A Common Stock [Member]
Dec. 31, 2010
2010 Plan [Member]
Class A Common Stock [Member]
Sep. 30, 2012
Stock Options [Member]
Dec. 31, 2010
Stock Options [Member]
Sep. 30, 2012
Stock Options [Member]
2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Shares reserved for future issuance                 28,500,000   10,000,000      
Common stock, par value (in usd per share)         $ 0.0001 $ 0.0001 $ 0.0001              
Options granted to date     706,644             964,144        
Shares available for grant                           9,039,574
Weighted-average remaining contractual life of all options expected to vest     8 years 4 months 28 days                      
Total intrinsic value of options exercised     $ 11,714,891                      
Exercise of stock options (in shares)     1,151,327         1,151,327            
Options exercised average exercise price (in usd per share)     $ 2.620         $ 2.62            
Proceeds from exercises of options 1,216,985 905,557 3,016,256 4,907,645                    
Options expiration period                       10 years    
Options vesting period                       5 years 5 years  
Options cliff vesting percentage                         20.00%  
Options ratable vesting percentage                       20.00% 5.00%  
Options ratable vesting frequency                       1 year 3 months  
Options postemployment exercisable period                       90 days    
Stock-based compensation expense 853,866 432,624 2,527,926 2,027,200                    
Non-vested stock options unrecognized compensation expense                       $ 7,541,614    
Non-vested stock options unrecognized compensation expense, weighted-average period of recognition                       3 years 4 months 10 days    
Cliff vesting period                         1 year  
Ratable vesting period                       5 years