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Leases - Narrative (Details)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2019
ft²
lease
Dec. 31, 2019
USD ($)
ft²
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Mar. 31, 2019
Operating Leased Assets [Line Items]          
Lessee, operating lease, area of land under lease 13,500        
Weighted-average remaining lease term 8 years 2 months 8 years 2 months      
Lease, cost | $   $ 3.2 $ 3.4 $ 2.5  
Number of lease agreements entered into | lease 2        
Minimum          
Operating Leased Assets [Line Items]          
Weighted-average remaining lease term         3 years 10 months 31 days
Maximum          
Operating Leased Assets [Line Items]          
Weighted-average remaining lease term         9 years 10 months 19 days
San Diego, California          
Operating Leased Assets [Line Items]          
Lessee, operating lease, area of land under lease   82,200      
Plymouth Meeting, Pennsylvania          
Operating Leased Assets [Line Items]          
Lessee, operating lease, area of land under lease   57,360