Summary of Significant Accounting Policies - Schedule of Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Change In The Allowance For Doubtful Accounts
Balance, beginning of period	$ 12,711	$ 9,049	$ 9,049
Add: provision for doubtful accounts	5,884	7,231	10,515
Less: write-offs, net of recoveries and other adjustments	(6,484)	(5,704)	(7,314)
Balance, end of period	$ 12,111	11,037	12,711	$ 9,049
Accounting Standards Update [Extensible List]	ASC 326			ASC 326
Cumulative Effect, Period Of Adoption, Adjustment | ASC 326
Change In The Allowance For Doubtful Accounts
Balance, beginning of period	$ 0	$ 461	461
Balance, end of period			$ 0	$ 461