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

Basis of Presentation and Summary of Significant Accounting Policies - Stock-based compensation (Details)

v3.21.2
Basis of Presentation and Summary of Significant Accounting Policies - Stock-based compensation (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
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]              
Stock-based compensation expense $ 4,848 $ 1,619 $ 12,100 $ 3,561 $ 20,527 $ 1,680 $ 1,442
General and administrative              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense $ 2,186 $ 1,102 $ 6,404 $ 2,227 20,527 1,680 1,442
Restricted Stock Units (RSUs)              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense           $ 100 $ 100
Restricted Stock Units (RSUs) | General and administrative              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense         $ 700