Shareholders' Equity - Reserved Ordinary Shares (Details) - shares	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jul. 23, 2018
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	3,826,869		3,020,460
Equity Incentive Plan, 2018
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,709,148	2,250,000	1,015,148	1,500,000
Employee Share Purchase Plan, 2018
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	287,000		100,000	100,000
Option on Securities
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,536,422		1,486,363
Restricted Stock
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	269,138		314,123
Rockport Warrants
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	25,161		104,826