Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details)

v3.10.0.1
Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Redeemable Convertible Preferred Stock Warrant Liability    
Liabilities:    
Total $ 867 $ 1,708
Fair Value Measurements Recurring    
Assets:    
Total 123,223 18,960
Liabilities:    
Total 867 1,708
Fair Value Measurements Recurring | Redeemable Convertible Preferred Stock Warrant Liability    
Liabilities:    
Total 867 1,708
Fair Value Measurements Recurring | Level 1    
Assets:    
Total 31,879 6,578
Liabilities:    
Total 0 0
Fair Value Measurements Recurring | Level 1 | Redeemable Convertible Preferred Stock Warrant Liability    
Liabilities:    
Total 0 0
Fair Value Measurements Recurring | Level 2    
Assets:    
Total 91,344 12,382
Liabilities:    
Total 0 0
Fair Value Measurements Recurring | Level 2 | Redeemable Convertible Preferred Stock Warrant Liability    
Liabilities:    
Total 0 0
Fair Value Measurements Recurring | Level 3    
Assets:    
Total 0 0
Liabilities:    
Total 867 1,708
Fair Value Measurements Recurring | Level 3 | Redeemable Convertible Preferred Stock Warrant Liability    
Liabilities:    
Total 867 1,708
Fair Value Measurements Recurring | Money Market Funds    
Assets:    
Total 31,879 6,578
Fair Value Measurements Recurring | Money Market Funds | Level 1    
Assets:    
Total 31,879 6,578
Fair Value Measurements Recurring | Money Market Funds | Level 2    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Money Market Funds | Level 3    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Commercial Paper    
Assets:    
Total 34,939 7,689
Fair Value Measurements Recurring | Commercial Paper | Level 1    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Commercial Paper | Level 2    
Assets:    
Total 34,939 7,689
Fair Value Measurements Recurring | Commercial Paper | Level 3    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Corporate Debt Securities    
Assets:    
Total 15,774 800
Fair Value Measurements Recurring | Corporate Debt Securities | Level 1    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Corporate Debt Securities | Level 2    
Assets:    
Total 15,774 800
Fair Value Measurements Recurring | Corporate Debt Securities | Level 3    
Assets:    
Total 0 0
Fair Value Measurements Recurring | Asset-backed Securities    
Assets:    
Total 16,864  
Fair Value Measurements Recurring | Asset-backed Securities | Level 1    
Assets:    
Total 0  
Fair Value Measurements Recurring | Asset-backed Securities | Level 2    
Assets:    
Total 16,864  
Fair Value Measurements Recurring | Asset-backed Securities | Level 3    
Assets:    
Total 0  
Fair Value Measurements Recurring | U.S. Government Agency Securities    
Assets:    
Total 23,767 3,893
Fair Value Measurements Recurring | U.S. Government Agency Securities | Level 1    
Assets:    
Total 0 0
Fair Value Measurements Recurring | U.S. Government Agency Securities | Level 2    
Assets:    
Total 23,767 3,893
Fair Value Measurements Recurring | U.S. Government Agency Securities | Level 3    
Assets:    
Total $ 0 $ 0