Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Leases (Details)

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Commitments and Contingencies - Leases (Details) - Chesterbrook, Pennsylvania
$ in Millions
Oct. 02, 2020
Oct. 11, 2018
ft²
$ / ft²
Dec. 31, 2020
USD ($)
ft²
Dec. 31, 2019
USD ($)
Leases        
Number of square feet of space leased on the first floor     8,231  
Number of square feet of space leased on the second floor     40,565  
Deferred rent | $     $ 0.0 $ 0.0
Sublease Agreements | Vanguard Group, Inc        
Leases        
Number of square feet of space being subleased on second floor   40,565    
Initial term of sublease   37 months    
Term of optional sublease extension 3 years      
Term of second optional sublease extension   3 years    
Amount per square foot less for rent during months 2 to 13 | $ / ft²   0.50    
Amount per square foot for rent after month 14 | $ / ft²   1.00