Organization, Basis of Presentation and Liquidity - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) numberOfPrograms numberOfDivestitures segment	Dec. 31, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of late-stage development programs | numberOfPrograms	2
Number of operating segments | segment	1
Total cash, cash equivalents and short-term investments, estimated fair value	$ 525,167	$ 251,155
Number of discrete business divestitures | numberOfDivestitures	2
Accumulated deficit	$ 1,254,670	$ 1,115,457