Stockholders' Equity and Stock-Based Compensation - Stock Option Plan Schedule 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 Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based payment arrangement, expense	$ 7,353	$ 4,420	$ 13,897	$ 8,579
Research and Development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based payment arrangement, expense	2,584	2,253	5,026	4,332
General and Administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based payment arrangement, expense	$ 4,769	$ 2,167	$ 8,871	$ 4,247