Annual report pursuant to Section 13 and 15(d)

Shareholders' (Deficit) / Equity - Additional Information (Details)

Shareholders' (Deficit) / Equity - Additional Information (Details) $ / shares in Units, € in Thousands, $ in Thousands					12 Months Ended
	Feb. 16, 2018 USD ($) $ / shares shares	May 18, 2017 USD ($) $ / shares shares	Dec. 16, 2016 USD ($) $ / shares shares	Nov. 18, 2015 USD ($) $ / shares shares	Dec. 31, 2019 Vote $ / shares shares	Dec. 31, 2018 $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2019 EUR (€) shares	Aug. 19, 2019 USD ($) shares	Aug. 19, 2019 EUR (€) shares	Jul. 15, 2019 USD ($) shares	Jul. 15, 2019 EUR (€) shares	Dec. 14, 2018 USD ($) shares	Dec. 14, 2018 EUR (€) shares	May 30, 2018 $ / shares shares	May 29, 2018 shares	May 15, 2018 $ / shares	Mar. 13, 2018 $ / shares shares	Mar. 12, 2018 $ / shares	Feb. 15, 2018 shares	Dec. 09, 2016 $ / shares shares	Oct. 14, 2015 $ / shares shares
Class Of Stock [Line Items]
Ordinary shares, shares authorized	44,557,606	7,956,715		3,659,453	50,000,000	50,000,000									50,000,000			44,557,606				413,110
Ordinary shares, shares issued					14,868,973	14,352,046												413,110				413,110
Ordinary shares, par value \| $ / shares	$ 0.01	$ 0.01		$ 0.01	$ 0.01	$ 0.01									$ 0.01			$ 0.001	$ 0.0001			$ 0.01
Share consolidation basis nominal value per share \| $ / shares																	$ 0.01571
Share consolidation basis, Renominalisation value per share \| $ / shares																	0.01
Increase in common stock, shares authorized																5,442,394				36,600,891
Number of vote per common share \| Vote					1
Common stock rights and preferences					The holders of ordinary shares have no preemptive or other subscription rights, and there are no redemption or sinking fund provisions with respect to such shares
Preferred stock, conversion basis						one-for-one
Undesignated Preferred Shares
Class Of Stock [Line Items]
Undesignated preferred shares, par value \| $ / shares															$ 0.01
Undesignated preferred shares, authorized															100,000,000
Undesignated preferred shares in issue					0	0
Series A Convertible Preferred Shares
Class Of Stock [Line Items]
Share consolidation basis nominal value per share \| $ / shares																	0.01571
Share consolidation basis, Renominalisation value per share \| $ / shares																	0.01
Temporary equity, shares authorized				3,022,915														3,032,463			9,548
Temporary equity, par value \| $ / shares				$ 0.01														$ 0.001	0.0001		$ 0.01
Temporary equity, shares issued			1,518,137	1,514,320														3,032,457
Temporary equity shares price per share \| $ / shares			$ 15.71	$ 15.71
Gross cash proceeds from Issuance of convertible preferred stock \| $			$ 20,851	$ 20,701
Series A Convertible Preferred Shares \| Founders
Class Of Stock [Line Items]
Conversion of debt amount \| $				$ 90
Convertible preferred stock issued upon conversion				5,728
Series A Convertible Preferred Shares \| Pfizer License Agreement
Class Of Stock [Line Items]
Temporary equity, shares issued				190,961
Temporary equity, additional shares issued			190,961
Series B-1 Convertible Preferred Shares
Class Of Stock [Line Items]
Share consolidation basis nominal value per share \| $ / shares																	0.01571
Share consolidation basis, Renominalisation value per share \| $ / shares																	$ 0.01
Temporary equity, shares authorized		2,654,215
Temporary equity, par value \| $ / shares		$ 0.01
Temporary equity, shares issued		2,654,206
Temporary equity shares price per share \| $ / shares		$ 17.28
Gross cash proceeds from Issuance of convertible preferred stock \| $		$ 45,867
Series B-2 Convertible Preferred Shares
Class Of Stock [Line Items]
Temporary equity, shares authorized	2,147,278	1,042,728
Temporary equity, par value \| $ / shares	$ 0.01	$ 0.01
Temporary equity, shares issued	1,709,650
Temporary equity shares price per share \| $ / shares	$ 18.85
Gross cash proceeds from Issuance of convertible preferred stock \| $	$ 32,230
Series B Convertible Preferred Shares
Class Of Stock [Line Items]
Temporary equity, shares authorized																		4,801,493
Temporary equity, par value \| $ / shares																		$ 0.001	$ 0.0001
Temporary equity, shares issued																		4,363,856
Supplier
Class Of Stock [Line Items]
Common stock, maximum shares authorized for subscription													700,000	700,000
Common stock, shares subscribed but unissued							199,056	199,056	245,493	245,493	17,222	17,222	190,615	190,615
Issuance of ordinary shares under subscription agreement \| $							$ 1,260		$ 1,670		$ 110		$ 1,360
Payment receivable upon common stock subscription agreement							$ 1,260	€ 1,150	$ 1,670	€ 1,500	$ 110	€ 100	$ 1,360	€ 1,200