Shareholders' Equity - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 20,787	$ 12,589	$ 42,354	$ 23,720
Research and development expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	11,457	6,611	23,305	11,768
General and administrative expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 9,330	$ 5,978	$ 19,049	$ 11,952