Quarterly report pursuant to Section 13 or 15(d)

Stock Incentive Plan (Narrative) (Details)

v2.4.0.8
Stock Incentive Plan (Narrative) (Details) (USD $)
 3 Months Ended 9 Months Ended 9 Months Ended 35 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2010
Sep. 30, 2013
Class A Common Stock [Member]
Dec. 31, 2012
Class A Common Stock [Member]
Sep. 30, 2013
2000 Plan [Member]
Dec. 31, 2010
2000 Plan [Member]
Mar. 31, 2013
2010 Plan [Member]
Class A Common Stock [Member]
Dec. 31, 2010
2010 Plan [Member]
Class A Common Stock [Member]
Sep. 30, 2013
Stock Options [Member]
Dec. 31, 2010
Stock Options [Member]
Sep. 30, 2013
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 (in shares)     563,360             1,527,504        
Shares available for grant                           8,566,927
Weighted-average remaining contractual life of all options expected to vest     8 years 5 months 27 days                      
Total intrinsic value of options exercised     $ 2,855,548                      
Exercise of stock options (in shares)     507,919         507,919            
Options exercised average exercise price (in usd per share)     $ 3.300         $ 3.300            
Proceeds from exercises of options 426,294 1,216,985 1,676,046 3,016,256                    
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%  
Vesting frequency                         3 months  
Options postemployment exercisable period                       90 days    
Stock-based compensation expense 789,416 853,866 2,125,276 2,527,926                    
Non-vested stock options unrecognized compensation expense                       $ 6,612,695    
Non-vested stock options unrecognized compensation expense, weighted-average period of recognition                       2 years 11 months 5 days