Common Stock - Shares of Stock Issued and Reserved (Details) - shares	Dec. 31, 2018	Oct. 16, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock outstanding (in shares)	24,450,757		3,603,140
Redeemable convertible preferred stock outstanding (in shares)	0		11,871,578	11,330,704
Stock options outstanding (in shares)	2,641,198		3,001,929
Stock options outstanding, common stock equivalents (in shares)			3,001,929
Stock options available for grant (in shares)	2,497,082		29,654
Warrants to purchase shares of stock (in shares)			280,876
Total issued and reserved for issuance (in shares)	29,760,595		18,787,177
Total issued and reserved for issuance, common stock equivalents (in shares)			18,986,360
Series 1 Common Stock
Class of Stock [Line Items]
Common stock outstanding (in shares)			3,112,955
Series 2 Common Stock
Class of Stock [Line Items]
Common stock outstanding (in shares)			490,185
Warrants to purchase shares of stock (in shares)	118,122	160,657	124,326
Warrants to purchase shares of stock, common stock equivalents (in shares)			124,326
Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Redeemable convertible preferred stock outstanding (in shares)	0		11,871,578
Redeemable convertible preferred stock outstanding, common stock equivalents (in shares)			12,066,654
Warrants to purchase shares of stock (in shares)	0		156,550
Warrants to purchase shares of stock, common stock equivalents (in shares)			160,657
Restricted Stock Units
Class of Stock [Line Items]
Restricted stock units outstanding (in shares)	53,436		0