Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended			6 Months Ended	12 Months Ended
	Jul. 31, 2018	Jan. 31, 2021	Dec. 31, 2020	May 31, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 25, 2019	Mar. 31, 2018
Stockholders' Equity
Gross proceeds from sale of stock						$ 7,520	$ 27,945	$ 24,219
Net proceeds from sale of stock				$ 35,200
Public offering
Stockholders' Equity
Number of shares issued			6,000,000			6,000,000
Shares issued, price per share			$ 2.50			$ 2.50
Gross proceeds from sale of stock			$ 15,000			$ 15,000
Net proceeds from sale of stock			$ 13,300			13,300
Public offering | Ordinary Shares
Stockholders' Equity
Number of shares issued	1,818,181
Shares issued, price per share	$ 27
Gross proceeds from sale of stock	$ 50,000
Net proceeds from sale of stock	$ 46,300
Purchase agreement
Stockholders' Equity
Number of shares issued				4,144,537
Number of ordinary shares that can be purchased by warrant holders				4,144,537
Share and warrant price				$ 9.1686
Gross proceeds from sale of stock				$ 38,000
Net proceeds from sale of stock				$ 35,200
Cantor Fitzgerald and Co. | At-the-market offering | Ordinary Shares
Stockholders' Equity
Number of shares issued					1,031,619
Gross proceeds from sale of stock					$ 37,800
Net proceeds from sale of stock					36,300
Value of shares unsold at termination date					12,200
Maximum aggregate gross proceeds under the sales agreement										$ 50,000
Jefferies LLC | At-the-market offering
Stockholders' Equity
Gross proceeds from sale of stock		$ 16,300				21,900
Net proceeds from sale of stock		$ 11,500				$ 20,400
Maximum aggregate gross proceeds under the sales agreement					$ 50,000				$ 50,000
Jefferies LLC | At-the-market offering | Ordinary Shares
Stockholders' Equity
Number of shares issued		3,933,350				1,992,390
Purchasers | Purchase agreement
Stockholders' Equity
Number of shares issued				4,144,537			1,379,310
Number of ordinary shares that can be purchased by warrant holders				4,144,537			1
Share and warrant price				$ 9.1686			$ 14.50
Warrants outstanding			4,059,532			4,059,532
Per share exercise price of right			$ 7.92			$ 7.92
Term			2 years			2 years
Gross proceeds from sale of stock							$ 20,000
Net proceeds from sale of stock							$ 18,300
Purchasers | Purchase agreement | Warrants Issued In December 2019
Stockholders' Equity
Warrants outstanding			1,379,310			1,379,310
Per share exercise price of right			$ 19.00			$ 19.00
Term			3 years			3 years
Purchasers | Purchase agreement | Warrants Issued In May 2020
Stockholders' Equity
Warrants outstanding			4,059,532			4,059,532
Per share exercise price of right			$ 7.92			$ 7.92
Term			2 years			2 years
Estimate | Jefferies LLC | At-the-market offering
Stockholders' Equity
Number of shares issued		3,933,350
Net proceeds from sale of stock		$ 11,500
Estimate | Jefferies LLC | At-the-market offering | Maximum
Stockholders' Equity
Gross proceeds from sale of stock		$ 16,300