Financial Instruments and Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
ASSETS
Total assets	$ 111,801	$ 21,680
Liabilities:
Total liabilities		313
Convertible Preferred Stock Warrants Liability
Liabilities:
Total liabilities		313
Money Market Funds
ASSETS
Total assets	111,801	21,680
Level 1
ASSETS
Total assets	111,801	21,680
Level 1 | Money Market Funds
ASSETS
Total assets	$ 111,801	21,680
Level 3
Liabilities:
Total liabilities		313
Level 3 | Convertible Preferred Stock Warrants Liability
Liabilities:
Total liabilities		$ 313