Nature of Business - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net Loss	$ 19,486	$ 19,793	$ 53,908	$ 55,709	$ 75,400	$ 62,300	$ 54,000
Accumulated deficit	(346,891)		(346,891)		(292,983)
Cash and cash equivalents	$ 93,133	$ 33,364	$ 93,133	$ 33,364	$ 41,441	$ 49,886