Share-Based Payments - 2019 Inducement Share Incentive Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 12, 2019
Weighted average exercise price in $ per share
Share-based compensation expense	$ 9,748,000	$ 5,154,000	$ 5,732,000
2019 Inducement Plan
Options
Granted (in shares)	703,150
Forfeited (in shares)	(97,500)
Outstanding at end of year (in shares)	605,650
Weighted average exercise price in $ per share
Granted (in dollars per share)	$ 2.22
Forfeited (in dollars per share)	2.69
Outstanding balance at end of year (in dollars per share)	$ 2.14
Share-based compensation expense	$ 77,000
2019 Inducement Plan | Ordinary Shares
Share-Based Payments
Shares reserved for future issuance	1,394,350			2,000,000
2019 Inducement Plan | Stock Options
Share-Based Payments
Exercise period	10 years
Weighted average exercise price in $ per share
Weighted-average grant date fair value (in dollars per share)	$ 1.30
Fair Value Assumptions
Expected term of options (in years)	6 years 1 month 6 days
Weighted-average remaining contractual life	9 years 7 months 6 days
Unrecognized compensation expense
Total unrecognized compensation related to unvested options	$ 700,000
Recognition period	3 years 3 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)	1.40%
2019 Inducement Plan | Stock Options | Maximum
Fair Value Assumptions
Expected volatility (as a percent)	63.70%
Risk-free interest rate (as a percent)	2.30%
2019 Inducement Plan | SARs
Share-Based Payments
Exercise period	10 years