Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Details)

Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, € in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Segment $ / shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Dec. 31, 2020 EUR (€)	Oct. 27, 2020 $ / shares	Jan. 01, 2019 USD ($)	May 30, 2018 $ / shares	Mar. 13, 2018 $ / shares	Mar. 12, 2018 $ / shares	Feb. 16, 2018 $ / shares	May 18, 2017 $ / shares	Nov. 18, 2015 $ / shares	Oct. 14, 2015 $ / shares
Accounting Policies [Line Items]
Ordinary shares, par value \| $ / shares			$ 0.01	$ 0.01						$ 0.01	$ 0.001	$ 0.0001	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Research and development funding arrangement, sub award granted	$ 1,500,000
Cost reimbursement arrangement recognition period	20 months
Cost reimbursement arrangement recognition beginning period	2017-08
Revenue		$ 37,000	$ 0	$ 37,000	$ 869,000
Type of Revenue [Extensible List]			us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Short-term investments			$ 0
Recognized income tax positions measured at largest amount greater than percentage of being realized			50.00%
Percentage elimination of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income			80.00%
Percentage deduction of interest of adjusted taxable income plus business interest income by tax payers			50.00%
Number of business segments \| Segment			1
Defined Contribution Plan, Tax Status [Extensible List]					us-gaap:QualifiedPlanMember
Defined benefit plan, contribution by employer					$ 114,000
Inventory			$ 0	$ 0
Milestone payments			0
Right-of-use asset			5,261,000	7,144,000
Lease liability			$ 5,745,000	$ 7,328,000
ASU 2016-02
Accounting Policies [Line Items]
Right-of-use asset									$ 7,600,000
Lease liability									$ 7,800,000
U.S. Tax Authority
Accounting Policies [Line Items]
Federal statutory tax rate			21.00%	21.00%	21.00%	34.00%
October Offering
Accounting Policies [Line Items]
Ordinary shares, par value \| $ / shares			$ 0.01					$ 0.01
June 3 SPA
Accounting Policies [Line Items]
Ordinary shares, par value \| $ / shares			0.01
June 30 SPA
Accounting Policies [Line Items]
Ordinary shares, par value \| $ / shares			$ 0.01
Tax Cuts and Jobs Act of 2017
Accounting Policies [Line Items]
Percentage deduction of interest of adjusted taxable income plus business interest income by tax payers			30.00%
Certificates Of Deposit
Accounting Policies [Line Items]
Restricted cash			$ 90,000
Warrant Issued \| October Offering
Accounting Policies [Line Items]
Restricted cash			182,000
Warrant Issued \| June 3 SPA
Accounting Policies [Line Items]
Restricted cash			17,000
Warrant Issued \| June 30 SPA
Accounting Policies [Line Items]
Restricted cash			19,000
Maximum
Accounting Policies [Line Items]
Cash, FDIC insured amount			250,000
Cash, DGS insured amount			$ 122,000				€ 100
Net opertaing loss carry back period			5 years
Defined contribution plan, employee minimum percentage of total plan assets			60.00%
Defined contribution plan, maximum deferral rate			3.00%