Common Stock (Details) - shares	Mar. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)	11,719,565	12,067,162
Stock options
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)	7,378,068	7,588,405
Restricted stock units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)	102,498	0
2018 Incentive Award Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)	3,436,451	3,556,507
2018 Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)	802,548	922,250