Unpaid claims - Additional information (Details) $ in Thousands |
9 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
|
Sep. 30, 2021
USD ($)
|
Sep. 30, 2020
USD ($)
|
Dec. 31, 2020
USD ($)
|
Dec. 31, 2019
USD ($)
|
Dec. 31, 2018
USD ($)
|
|
| Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract] | |||||
| Unpaid claims | $ 140,210 | $ 93,615 | $ 103,976 | $ 77,886 | $ 41,660 |
| Prior years | $ 109,362 | $ 55,559 | $ 63,039 | $ 37,742 | |
| Ratio of current year medical claims paid as a percent of current year net medical claims | 0.882 | 0.796 | 0.830 | 0.831 | |