Net Loss per Share - Antidilutive Securities Excluded from Computation (Details) - shares	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	2,096,348	8,643,868
Stock Options
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	2,096,348	1,168,938
Redeemable convertible preferred stock
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)		7,474,930

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration