Summary of Significant Accounting Policies - Impact of Adoption of ASC 606 on Previously Reported Amounts of Consolidated Statements of Operations and Comprehensive Loss (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Collaboration revenue	$ 1,666	$ 5,322
Loss from operations	(109,943)	(59,926)
Net loss	$ (103,916)	$ (55,577)
Net loss per share attributable to common stockholders-basic and diluted	$ (2.47)	$ (1.95)
ASC 606 | As Originally Reported Under ASC 605
Collaboration revenue		$ 3,684
Loss from operations		(61,564)
Net loss		$ (57,215)
Net loss per share attributable to common stockholders-basic and diluted		$ (2.00)
ASC 606 | Effect of Change
Collaboration revenue		$ 1,638
Loss from operations		1,638
Net loss		$ 1,638
Net loss per share attributable to common stockholders-basic and diluted		$ 0.05