Convertible Preferred Stock and Stockholders’ Equity (Deficit) - Employee Stock Purchase Plan Narrative (Details) - shares	6 Months Ended
	Jun. 30, 2019	Aug. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Common stock initially reserved for future issuance (shares)	6,374,148
Number of common stock purchased under plan (shares)	66,155
2018 Employee Stock Purchase Plan
Subsidiary, Sale of Stock [Line Items]
Common stock initially reserved for future issuance (shares)		175,000
Incremental rate at which the shares reserved for issuance increase	1.00%
2018 Employee Stock Purchase Plan | Maximum
Subsidiary, Sale of Stock [Line Items]
Common stock initially reserved for future issuance (shares)		220,000