Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Ordinary Shares American Depositary Shares Ionis Share Purchase Agreement	Ordinary Shares	Additional Paid-in Capital American Depositary Shares Ionis Share Purchase Agreement	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	American Depositary Shares Ionis Share Purchase Agreement	Total
Beginning balance at Dec. 31, 2019		$ 227		$ 195,056	$ (1,535)	$ (100,550)		$ 93,198
Beginning balance (in shares) at Dec. 31, 2019		17,993,701
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options				2				2
Issuance of ADSs upon exercise of share options (in shares)		1,071
Issuance of ordinary shares upon exercise of warrants (in shares)		21,435
Share based compensation expense				2,121				2,121
Foreign currency translation adjustment					(2,184)			(2,184)
Net loss						(11,324)		(11,324)
Ending balance at Mar. 31, 2020		$ 227		197,179	(3,719)	(111,874)		81,813
Ending balance (in shares) at Mar. 31, 2020		18,016,207
Beginning balance at Dec. 31, 2019		$ 227		195,056	(1,535)	(100,550)		93,198
Beginning balance (in shares) at Dec. 31, 2019		17,993,701
Increase (decrease) in shareholders' equity (deficit)
Foreign currency translation adjustment								(1,442)
Net loss								(33,577)
Ending balance at Sep. 30, 2020		$ 264		246,391	(2,977)	(134,127)		109,551
Ending balance (in shares) at Sep. 30, 2020		20,935,853
Beginning balance at Mar. 31, 2020		$ 227		197,179	(3,719)	(111,874)		81,813
Beginning balance (in shares) at Mar. 31, 2020		18,016,207
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options				9				9
Issuance of ADSs upon exercise of share options (in shares)		4,000
Issuance of ordinary shares upon exercise of warrants		$ 1						1
Issuance of ordinary shares upon exercise of warrants (in shares)		71,450
Share based compensation expense				1,319				1,319
Foreign currency translation adjustment					(1)			(1)
Net loss						(12,115)		(12,115)
Ending balance at Jun. 30, 2020		$ 228		198,507	(3,720)	(123,989)		71,026
Ending balance (in shares) at Jun. 30, 2020		18,091,657
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options				87				87
Issuance of ADSs upon exercise of share options (in shares)		13,483
Issuance of ADSs, net of commissions and offering expenses		$ 36		46,287				46,323
Issuance of ADSs, net of commissions and offering expenses (in shares)		2,830,713
Share based compensation expense				1,510				1,510
Foreign currency translation adjustment					743			743
Net loss						(10,138)		(10,138)
Ending balance at Sep. 30, 2020		$ 264		246,391	(2,977)	(134,127)		109,551
Ending balance (in shares) at Sep. 30, 2020		20,935,853
Beginning balance at Dec. 31, 2020		$ 266		249,947	(3,193)	(151,560)		$ 95,460
Beginning balance (in shares) at Dec. 31, 2020		21,094,557						21,094,557
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options		$ 1		283				$ 284
Issuance of ADSs upon exercise of share options (in shares)		63,545
Issuance of ADSs, net of commissions and offering expenses		$ 33		58,742				58,775
Issuance of ADSs, net of commissions and offering expenses (in shares)		2,358,485
Share based compensation expense				3,821				3,821
Foreign currency translation adjustment					(58)			(58)
Net loss						(16,191)		(16,191)
Ending balance at Mar. 31, 2021		$ 300		312,793	(3,251)	(167,751)		142,091
Ending balance (in shares) at Mar. 31, 2021		23,516,587
Beginning balance at Dec. 31, 2020		$ 266		249,947	(3,193)	(151,560)		$ 95,460
Beginning balance (in shares) at Dec. 31, 2020		21,094,557						21,094,557
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options (in shares)								446,600
Net loss								$ (48,782)
Ending balance at Sep. 30, 2021		$ 329		374,029	(3,193)	(200,342)		$ 170,823
Ending balance (in shares) at Sep. 30, 2021		25,595,326						25,595,326
Beginning balance at Mar. 31, 2021		$ 300		312,793	(3,251)	(167,751)		$ 142,091
Beginning balance (in shares) at Mar. 31, 2021		23,516,587
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options		$ 2		1,573				1,575
Issuance of ADSs upon exercise of share options (in shares)		125,666
Issuance of ADSs, net of commissions and offering expenses		$ 7		13,970				13,977
Issuance of ADSs, net of commissions and offering expenses (in shares)		482,299
Share based compensation expense				2,575				2,575
Foreign currency translation adjustment					(255)			(255)
Net loss						(17,913)		(17,913)
Ending balance at Jun. 30, 2021		$ 309		330,911	(3,506)	(185,664)		142,050
Ending balance (in shares) at Jun. 30, 2021		24,124,552
Increase (decrease) in shareholders' equity (deficit)
Issuance of ADSs upon exercise of share options		$ 4		3,045				3,049
Issuance of ADSs upon exercise of share options (in shares)		257,389
Issuance of ADSs, net of commissions and offering expenses	$ 4	$ 12	$ 7,554	29,831			$ 7,558	29,843
Issuance of ADSs, net of commissions and offering expenses (in shares)	282,485	930,900
Share based compensation expense				2,688				2,688
Foreign currency translation adjustment					313			313
Net loss						(14,678)		(14,678)
Ending balance at Sep. 30, 2021		$ 329		$ 374,029	$ (3,193)	$ (200,342)		$ 170,823
Ending balance (in shares) at Sep. 30, 2021		25,595,326						25,595,326