Share-Based Payments - 2019 Inducement Share Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Mar. 12, 2019
Aggregate intrinsic value
Share-based compensation expense		$ 3,728	$ 2,011
2019 Inducement Plan
Share-Based Payments
Shares available for grant	2,000,000	2,000,000
Aggregate intrinsic value
Share-based compensation expense	$ 14	$ 14
Unrecognized compensation expense
Total unrecognized compensation related to unvested options	$ 300	$ 300
Recognition period		3 years 9 months 18 days
2019 Inducement Plan | Ordinary Shares
Share-Based Payments
Shares reserved for future issuance				2,000,000
2019 Inducement Plan | Stock Options
Options
Outstanding at beginning of year (in shares)		0
Granted (in shares)		205,150
Outstanding at end of year (in shares)	205,150	205,150
Weighted average exercise price in $ per share
Outstanding balance at beginning of year (in dollars per share)		$ 0.00
Granted (in dollars per share)		2.75
Outstanding balance at end of year (in dollars per share)	$ 2.75	$ 2.75
Aggregate intrinsic value
Aggregate intrinsic value, outstanding	$ 5	$ 5
Weighted-average grant date fair value (in dollars per share)		$ 1.87
Fair Value Assumptions
Expected term of options (in years)		6 years 1 month 6 days
Dividend yield (as a percent)		0.00%
Weighted-average remaining contractual life		9 years 9 months 18 days
2019 Inducement Plan | Stock Options | Minimum
Fair Value Assumptions
Expected volatility (as a percent)		61.60%
Risk-free interest rate (as a percent)		1.98%
2019 Inducement Plan | Stock Options | Maximum
Share-Based Payments
Exercise period		10 years
Fair Value Assumptions
Expected volatility (as a percent)		62.90%
Risk-free interest rate (as a percent)		2.34%
2019 Inducement Plan | SARs | Maximum
Share-Based Payments
Exercise period		10 years