Share-Based Compensation - Non-Cash Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-Based Compensation
Share-based compensation expense	$ 16,879	$ 7,330
Minimum
Share-Based Compensation
Requisite service period of award (in years)	3 years
Maximum
Share-Based Compensation
Requisite service period of award (in years)	4 years
Research and development expenses
Share-Based Compensation
Share-based compensation expense	$ 6,251	3,700
General and administrative expenses
Share-Based Compensation
Share-based compensation expense	$ 10,628	$ 3,630