License, Collaboration, and Funding Agreements - Genzyme Agreement (Details) - USD ($)			1 Months Ended		12 Months Ended
	Nov. 26, 2019	Apr. 12, 2019	Aug. 31, 2015	Aug. 31, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Stock issued (in shares)	3,666,667	5,670,000
Stock issued						$ 0	$ 0
Sale price (in dollars per share)	$ 12.00	$ 11.00
Genzyme Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments				$ 50,000
Payments to acquire process			$ 300,000
Stock issued (in shares)			107,371
Stock issued			$ 734,000
Sale price (in dollars per share)				$ 0.01
Milestone payments					$ 25,000,000.0
Payment on obligation under license agreement					$ 0	$ 0	$ 0