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	12,482		12,482
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	(36,675)			(36,675)
Ending balance (in shares) at Jun. 30, 2019		39,896,561
Ending balance at Jun. 30, 2019	302,807	$ 399	933,291	(630,883)
Beginning balance (in shares) at Mar. 31, 2019		39,864,561
Beginning balance at Mar. 31, 2019	312,130	$ 399	926,804	(615,073)
Share-based compensation	6,277		6,277
Issuance of ordinary shares upon exercise of stock options (in shares)		32,000
Issuance of ordinary shares upon exercise of stock options	210		210
Net loss	(15,810)			(15,810)
Ending balance (in shares) at Jun. 30, 2019		39,896,561
Ending balance at Jun. 30, 2019	302,807	$ 399	933,291	(630,883)
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	$ 11,223		11,223
Issuance of ordinary shares upon exercise of stock options (in shares)	12,852	12,852
Issuance of ordinary shares upon exercise of stock options	$ 151		151
Net loss	(49,851)			(49,851)
Ending balance (in shares) at Jun. 30, 2020		39,911,413
Ending balance at Jun. 30, 2020	234,444	$ 399	955,781	(721,736)
Beginning balance (in shares) at Mar. 31, 2020		39,911,413
Beginning balance at Mar. 31, 2020	255,039	$ 399	950,094	(695,454)
Share-based compensation	5,687		5,687
Net loss	(26,282)			(26,282)
Ending balance (in shares) at Jun. 30, 2020		39,911,413
Ending balance at Jun. 30, 2020	$ 234,444	$ 399	$ 955,781	$ (721,736)