Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Total assets	$ 889,041,000		$ 889,041,000		$ 262,390,000
Total liabilities	260,121,000		260,121,000		41,669,000
Revenues	49,070,000	$ 0	93,768,000	$ 0
Restricted cash	400,000		400,000		500,000
Allowance for doubtful accounts	0		0		0
Allowance for contractual adjustments	700,000		700,000		$ 1,000,000
Concentration Risk [Line Items]
Impairment charge for intangible assets	0		0
Impairment charge for goodwill	0		0
Research and development	1,916,000	0	5,759,000	0
Advertising expense	1,100,000	$ 0	2,800,000	$ 0
VIE
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Total assets	4,500,000		4,500,000
Total liabilities	$ 4,000,000		4,000,000
Revenues			100,000
Expenses			$ 100,000
Customer Concentration Risk | Revenue from Contract with Customer Benchmark | One Customer
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%		20.00%
Customer Concentration Risk | Accounts Receivable | One Customer
Concentration Risk [Line Items]
Concentration risk, percentage			42.00%
Customer Concentration Risk | Accounts Receivable | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage					47.00%
Customer Concentration Risk | Accounts Receivable | Customer B
Concentration Risk [Line Items]
Concentration risk, percentage					27.00%