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Leases - Narrative (Details)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2021
USD ($)
ft²
Sep. 30, 2020
USD ($)
Dec. 31, 2019
ft²
agreement
Lessee, Lease, Description [Line Items]          
Lease cost | $ $ 852 $ 836 $ 2,500 $ 2,500  
Number of agreements | agreement         2
Minimum          
Lessee, Lease, Description [Line Items]          
Operating lease, remaining lease term 2 years 2 months 12 days   2 years 2 months 12 days    
Maximum          
Lessee, Lease, Description [Line Items]          
Operating lease, remaining lease term 8 years 3 months 18 days   8 years 3 months 18 days    
San Diego, California          
Lessee, Lease, Description [Line Items]          
Area leased (in square feet)     82,200    
Plymouth Meeting, Pennsylvania          
Lessee, Lease, Description [Line Items]          
Area leased (in square feet)     57,360   13,500