Summary of Significant Accounting Policies - Summary of Company's Financial Instruments Classification Within Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total financial liabilities	$ 52,355	$ 9,990
Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total financial liabilities	52,355	9,990
Convertible Preferred Stock Warrant Liability
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total financial liabilities	52,355	9,990
Convertible Preferred Stock Warrant Liability | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total financial liabilities	$ 52,355	$ 9,990