Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (30,608)	$ (21,846)	$ (16,259)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,083	1,023	515
Depreciation and amortization	960	712	332
Change in fair value of warrant liability	5,381	665	119
Changes in operating assets and liabilities:
Accounts receivable	4,909	(400)
Non-cash research and development expense			856
Research and development incentives receivable	(383)	(3,586)	(1,407)
Prepaid expenses and other current assets	(2,723)	(1,329)	(330)
Operating lease right‑of‑use assets	712
Other assets	(397)	(301)	(1,039)
Accounts payable	220	(169)	67
Accrued expenses and other current liabilities	(852)	2,557	1,267
Lease liabilities	(709)
Deferred revenue	(9,295)	(3,947)	14,081
Other long-term liabilities	1,089	543	383
Net cash used in operating activities	(28,613)	(26,078)	(1,415)
Cash used in investing activities:
Purchases of property and equipment	(1,555)	(1,186)	(1,113)
Net cash used in investing activities	(1,555)	(1,186)	(1,113)
Cash flows from financing activities:
Proceeds from issuance of ADSs in initial public offering, net of issuance costs	56,957	(576)
Proceeds from the exercise of share options and sale of ordinary shares	143	1	1
Proceeds from the exercise of warrants	6
Net cash provided by financing activities	58,440	25,430	57,876
Effect of exchange rate changes on cash	465	(2,449)	2,913
Net increase (decrease) in cash	28,737	(4,283)	58,261
Cash at beginning of period	63,380	67,663	9,402
Cash at end of period	92,117	63,380	67,663
Supplemental disclosure of cash flow information
Cash paid for income taxes	117	73
Cash paid for amounts included in the measurement of operating lease liabilities	891
Purchases of property and equipment included in accounts payable and accrued expenses	76
Advance billings on deferred revenue included in accounts receivable		5,045
Deferred initial public offering costs accrued but not paid		1,076
Conversion of convertible preferred shares to ordinary shares upon closing of the initial public offering	123,780
Reclassification of warrant liability to additional paid-in capital	10,021
Series B1 Convertible Preferred Shares
Cash flows from financing activities:
Proceeds from issuance of convertible preferred shares, net of issuance costs			$ 57,875
Series B2 Convertible Preferred Shares
Cash flows from financing activities:
Proceeds from issuance of convertible preferred shares, net of issuance costs	$ 1,334	26,005
Supplemental disclosure of cash flow information
Series B2 convertible preferred financing costs accrued but not paid		$ 249