General form of registration statement for all companies including face-amount certificate companies

Stock-Based Compensation - Additional information (Details)

v3.21.2
Stock-Based Compensation - Additional information (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Sep. 30, 2017
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Outstanding Ending balance     14,439   14,439   14,713 19,656 18,542
Weighted average grant date fair value (in dollars per share)         $ 12.85 $ 2.40 $ 2.67 $ 1.41 $ 0.51
Intrinsic value         $ 50,500 $ 500 $ 3,600 $ 300 $ 0
Stock-based compensation expense     $ 4,848 $ 1,619 12,100 $ 3,561 $ 20,527 $ 1,680 $ 1,442
Unrecognized stock-based compensation expense     $ 68,900   $ 68,900        
Weighted-average period over which unrecognized stock-based compensation expense are expected to be recognized         1 year 7 months 6 days        
Former Executive                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Repurchased and cancelled shares             2,606    
Former Executive | Additional Paid-in Capital                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Aggregate purchase price             $ 15,500    
Performance and Market Based Options                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Granted         0   600    
Outstanding Ending balance     3,433   3,433   3,433    
Repurchased and cancelled shares             956    
Incremental cash based compensation expenses             $ 14,500    
Market Based Restricted Stock Units                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Granted             167    
Vested             167    
Restricted Stock Units (RSUs)                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Granted 37 75     1,720   1,510    
Vested         322   185 38 38
Granted, Weighted average grant date fair value $ 3.72 $ 1.68     $ 30.88   $ 7.59    
Granted, Fair value $ 100 $ 100              
Stock-based compensation expense               $ 100 $ 100
Unrecognized stock-based compensation expense             $ 15,500    
Weighted-average period over which unrecognized stock-based compensation expense are expected to be recognized             1 year 3 months 18 days