CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
License revenue - related party	$ 2,473,705	$ 1,981,676	$ 6,683,281	$ 2,766,636
Operating expenses:
General and administrative	11,497,270	13,437,171	23,303,404	21,936,646
Research and development	16,202,065	9,771,754	24,285,405	22,747,983
Total operating expenses	27,699,335	23,208,925	47,588,809	44,684,629
Loss from operations	(25,225,630)	(21,227,249)	(40,905,528)	(41,917,993)
Other non-operating income (expense):
Foreign currency (loss) gain	(351,863)	283,175	(1,108,567)	3,001,575
Interest income	193,604	39,726	982,975	39,726
Interest expense	(34,045)	(9,454)	(68,011)	(19,028)
Loss before income taxes	(25,417,934)	(20,913,802)	(41,099,131)	(38,895,720)
Benefit for income taxes		91,390		91,390
Net loss	(25,417,934)	(20,822,412)	(41,099,131)	(38,804,330)
Other comprehensive income:
Foreign currency translation gain, net of tax of $0, for the three-month and six-month periods ended June 30, 2020, and $91,390 for the three-month and six-month periods ended June 30, 2019	517,592	1,579,882	4,463,516	446,199
Total comprehensive loss	(24,900,342)	(19,242,530)	(36,635,615)	(38,358,131)
Net loss	$ (25,417,934)	$ (20,822,412)	$ (41,099,131)	$ (38,804,330)
Basic and diluted net loss per ordinary share	$ (0.69)	$ (0.63)	$ (1.12)	$ (1.26)
Weighted-average number of ordinary shares outstanding	36,969,682	32,827,029	36,797,316	30,814,639