Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Ordinary Share	Additional Paid-in Capital	Retained Earnings
Cumulative adjustment to accumulated deficit upon adoption of ASC-842 | ASC-842	$ 3,787			$ 3,787
Beginning balance (in shares) at Dec. 31, 2018		39,863,711
Beginning balance at Dec. 31, 2018	322,998	$ 399	$ 920,594	(597,995)
Share-based compensation	18,298		18,298
Issuance of ordinary shares upon exercise of stock options (in shares)		32,850
Issuance of ordinary shares upon exercise of stock options	215		215
Net loss	(56,123)			(56,123)
Ending balance (in shares) at Sep. 30, 2019		39,896,561
Ending balance at Sep. 30, 2019	289,175	$ 399	939,107	(650,331)
Beginning balance (in shares) at Jun. 30, 2019		39,896,561
Beginning balance at Jun. 30, 2019	302,807	$ 399	933,291	(630,883)
Share-based compensation	5,816		5,816
Net loss	(19,448)			(19,448)
Ending balance (in shares) at Sep. 30, 2019		39,896,561
Ending balance at Sep. 30, 2019	289,175	$ 399	939,107	(650,331)
Beginning balance (in shares) at Dec. 31, 2019		39,898,561
Beginning balance at Dec. 31, 2019	272,921	$ 399	944,407	(671,885)
Share-based compensation	$ 16,806		16,806
Issuance of ordinary shares upon exercise of stock options (in shares)	22,852	22,852
Issuance of ordinary shares upon exercise of stock options	$ 215		215
Net loss	(80,428)			(80,428)
Ending balance (in shares) at Sep. 30, 2020		39,921,413
Ending balance at Sep. 30, 2020	209,514	$ 399	961,428	(752,313)
Beginning balance (in shares) at Jun. 30, 2020		39,911,413
Beginning balance at Jun. 30, 2020	234,444	$ 399	955,781	(721,736)
Share-based compensation	5,583
Issuance of ordinary shares upon exercise of stock options (in shares)		10,000
Issuance of ordinary shares upon exercise of stock options	64		64
Net loss	(30,577)			(30,577)
Ending balance (in shares) at Sep. 30, 2020		39,921,413
Ending balance at Sep. 30, 2020	$ 209,514	$ 399	$ 961,428	$ (752,313)