Fair Value Measurement - Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Liabilities:
Convertible preferred stock warrant liability	$ 17,008	$ 4,589
Recurring
Liabilities:
Convertible preferred stock warrant liability	17,008	4,589
Total	17,008	4,589
Recurring \| Level 3
Liabilities:
Convertible preferred stock warrant liability	17,008	4,589
Total	$ 17,008	$ 4,589

Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant