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Fair Value Measurements - Schedule of Fair Value of Company's Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Assets    
Total financial assets $ 54,120 $ 73,411
Level 1    
Assets    
Total financial assets 23,613 10,606
Level 2    
Assets    
Total financial assets 30,507 62,805
Money Market Funds    
Assets    
Total financial assets 23,613 10,606
Money Market Funds | Level 1    
Assets    
Total financial assets 23,613 10,606
U.S. Government Securities    
Assets    
Total financial assets 3,477 9,975
U.S. Government Securities | Level 2    
Assets    
Total financial assets 3,477 9,975
Corporate Notes    
Assets    
Total financial assets 11,286 16,499
Corporate Notes | Level 2    
Assets    
Total financial assets 11,286 16,499
Commercial Paper    
Assets    
Total financial assets 15,744 36,331
Commercial Paper | Level 2    
Assets    
Total financial assets $ 15,744 $ 36,331