Quarterly report pursuant to Section 13 or 15(d)

Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details)

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Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis $ 123,251 $ 18,960  
Unrealized Gains 1 0  
Unrealized Losses (29) 0  
Fair Value 123,223 18,960  
Less amounts classified as cash equivalents, Amortized Cost Basis (41,353) (22,020) $ (25,407)
Marketable Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 81,625 0  
Unrealized Gains 1 0  
Unrealized Losses (29) 0  
Fair Value 81,597 0  
Cash Equivalents      
Cash And Cash Equivalents [Line Items]      
Less amounts classified as cash equivalents, Amortized Cost Basis (41,626) (18,960)  
Less amounts classified as cash equivalents, Fair Value (41,626) (18,960)  
Money Market Funds      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 31,879 6,578  
Unrealized Gains 0 0  
Unrealized Losses 0 0  
Fair Value 31,879 6,578  
Commercial Paper      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 34,939 7,689  
Unrealized Gains 0 0  
Unrealized Losses 0 0  
Fair Value 34,939 7,689  
Corporate Debt Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 15,781 800  
Unrealized Gains 1 0  
Unrealized Losses (8) 0  
Fair Value 15,774 800  
Asset-backed Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 16,876    
Unrealized Gains 0    
Unrealized Losses (12)    
Fair Value 16,864    
U.S. Government Agencies      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 23,776 3,893  
Unrealized Gains 0 0  
Unrealized Losses (9) 0  
Fair Value $ 23,767 $ 3,893