Stock-Based Awards - Classification of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 10,609	$ 4,107	$ 17,603	$ 10,336
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	5,293	1,790	8,564	3,482
Selling, general, and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 5,316	$ 2,317	$ 9,039	$ 6,854