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Leases - Narrative (Details)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
ft²
Jun. 30, 2018
USD ($)
Lessee, Lease, Description [Line Items]        
Operating lease, weighted average remaining lease term 8 years 8 months   8 years 8 months  
Lease cost | $ $ 835 $ 941 $ 1,700 $ 1,600
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  
Minimum        
Lessee, Lease, Description [Line Items]        
Operating lease, weighted average remaining lease term 4 years 4 months 12 days   4 years 4 months 12 days  
Maximum        
Lessee, Lease, Description [Line Items]        
Operating lease, weighted average remaining lease term 10 years 5 months 18 days   10 years 5 months 18 days