Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock/Ordinary Shares	Additional paid in capital	Accumulated other comprehensive income	Accumulated deficit	Total
Stockholders' equity, beginning balance at Dec. 31, 2019	$ 95	$ 517,894	$ 27	$ (476,742)	$ 41,274
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2019	9,455
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock & ordinary shares		186			186
Issuance of common stock & ordinary shares (in shares)	48
Shares issued in connection with the vesting of restricted share units (in shares)	8
Equity transaction costs		(39)			(39)
Stock-based compensation expense		1,752			1,752
Net loss				(23,259)	(23,259)
Stockholders' equity, ending balance at Mar. 31, 2020	$ 95	519,793	27	(500,001)	19,914
Stockholders' equity, ending balance (in shares) at Mar. 31, 2020	9,511
Stockholders' equity, beginning balance at Dec. 31, 2019	$ 95	517,894	27	(476,742)	41,274
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2019	9,455
Consolidated Statements of Changes in Stockholders' Equity
Net loss					(38,700)
Stockholders' equity, ending balance at Jun. 30, 2020	$ 143	559,733	27	(515,442)	44,461
Stockholders' equity, ending balance (in shares) at Jun. 30, 2020	14,297
Stockholders' equity, beginning balance at Mar. 31, 2020	$ 95	519,793	27	(500,001)	19,914
Stockholders' equity, beginning balance (in shares) at Mar. 31, 2020	9,511
Consolidated Statements of Changes in Stockholders' Equity
Issuance of ordinary shares and warrants	$ 48	41,319			41,367
Issuance of ordinary shares and warrants (in shares)	4,758
Shares issued in connection with the vesting of restricted share units (in shares)	19
Shares issued in connection with the employee stock purchase plan		43			43
Shares issued in connection with the employee stock purchase plan (in shares)	9
Equity transaction costs		(2,709)			(2,709)
Stock-based compensation expense		1,287			1,287
Net loss				(15,441)	(15,441)
Stockholders' equity, ending balance at Jun. 30, 2020	$ 143	559,733	27	(515,442)	44,461
Stockholders' equity, ending balance (in shares) at Jun. 30, 2020	14,297
Stockholders' equity, beginning balance at Dec. 31, 2020	$ 211	579,123	27	(546,226)	33,135
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2020	21,079
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock & ordinary shares	$ 143	37,097			37,240
Issuance of common stock & ordinary shares (in shares)	14,294
Shares issued in connection with the vesting of restricted share units		1			1
Shares issued in connection with the vesting of restricted share units (in shares)	40
Equity transaction costs		(2,325)			(2,325)
Stock-based compensation expense		921			921
Net loss				(13,981)	(13,981)
Stockholders' equity, ending balance at Mar. 31, 2021	$ 354	614,817	27	(560,207)	54,991
Stockholders' equity, ending balance (in shares) at Mar. 31, 2021	35,413
Stockholders' equity, beginning balance at Dec. 31, 2020	$ 211	579,123	27	(546,226)	33,135
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2020	21,079
Consolidated Statements of Changes in Stockholders' Equity
Net loss					(25,735)
Stockholders' equity, ending balance at Jun. 30, 2021	$ 497	640,638	27	(571,961)	69,201
Stockholders' equity, ending balance (in shares) at Jun. 30, 2021	49,738
Stockholders' equity, beginning balance at Mar. 31, 2021	$ 354	614,817	27	(560,207)	54,991
Stockholders' equity, beginning balance (in shares) at Mar. 31, 2021	35,413
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock & ordinary shares	$ 142	25,997			26,139
Issuance of common stock & ordinary shares (in shares)	14,313
Shares issued in connection with the vesting of restricted share units	$ 1	(1)
Shares issued in connection with the vesting of restricted share units (in shares)	12
Equity transaction costs		(992)			(992)
Stock-based compensation expense		817			817
Net loss				(11,754)	(11,754)
Stockholders' equity, ending balance at Jun. 30, 2021	$ 497	$ 640,638	$ 27	$ (571,961)	$ 69,201
Stockholders' equity, ending balance (in shares) at Jun. 30, 2021	49,738