Fair Value Measurements - Financial Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Liabilities:
Total financial liabilities	$ 4,714	$ 1,104
Redeemable Convertible Preferred Stock Warrant Liability
Financial Liabilities:
Total financial liabilities	4,714	1,104
Level III
Financial Liabilities:
Total financial liabilities	4,714	1,104
Level III | Redeemable Convertible Preferred Stock Warrant Liability
Financial Liabilities:
Total financial liabilities	$ 4,714	$ 1,104