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Commitments and Contingencies - Narrative (Details)
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
agreement
Dec. 31, 2017
USD ($)
Feb. 17, 2012
Apr. 06, 2005
Loss Contingencies [Line Items]        
Lease agreement term (years)       8 years
Additional lease term (years) 5 years      
Rental expense | $ $ 1.6 $ 1.6    
Number of collaboration agreements | agreement 2      
Amended Lease        
Loss Contingencies [Line Items]        
Lease agreement term (years)     10 years