Shareholders' Equity - Reserved Ordinary Shares (Details) - shares	Sep. 30, 2020	Dec. 31, 2019	Jan. 01, 2019	Jul. 23, 2018
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	4,325,440	3,571,406
Equity Incentive Plan, 2018
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,747,383	1,312,648	3,000,000	1,500,000
Options to purchase shares
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	2,007,189	1,837,576
Restricted Stock
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	91,368	128,682
ESPP
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	474,000	287,000
Rockport Warrants
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	5,500	5,500