Related-Party Transactions - Number of Shares of Common Stock Purchased (Details) - USD ($)			12 Months Ended
	Dec. 18, 2019	Aug. 19, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Stock issued (in shares)			86,325,547
Shares issued, value			$ 30,942,000	$ 0	$ 10,000,000
Founders
Related Party Transaction [Line Items]
Consulting services expenses			$ 500,000	200,000	200,000
Timothy A. Springer, Ph.D. | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			4,000,000
Shares issued, value			$ 6,000,000
Entities affiliated with Polaris
Related Party Transaction [Line Items]
Stock issued (in shares)			666,666
Shares issued, value			$ 999,999
Chafen Lu (Timothy A. Springer’s wife)
Related Party Transaction [Line Items]
Stock issued (in shares)			66,666
Shares issued, value			$ 99,999
Jed Springer (Timothy A. Springer’s brother)
Related Party Transaction [Line Items]
Stock issued (in shares)			1,000
Shares issued, value			$ 1,500
December 2019 Financing
Related Party Transaction [Line Items]
Stock issued (in shares)	37,634,883
December 2019 Financing | TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.)
Related Party Transaction [Line Items]
Stock issued (in shares)			3,940,887
Shares issued, value			$ 6,000,000
December 2019 Financing | Carrie S. Cox | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			65,681
Shares issued, value			$ 99,999
December 2019 Financing | Timothy Barabe | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			65,681
Shares issued, value			$ 99,999
December 2019 Financing | Scott D. Myers | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			39,409
Shares issued, value			$ 60,000
Private Placement
Related Party Transaction [Line Items]
Shares issued, value			$ 5,715,000	$ 0	$ 47,114,000
Private Placement | Director
Related Party Transaction [Line Items]
Stock issued (in shares)		3,178,174
Private Placement | TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.) | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			1,100,000
Shares issued, value			$ 1,991,000
Private Placement | Scott D. Myers | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			41,436
Shares issued, value			$ 74,999
Private Placement | Timothy A. Springer, Ph.D. | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			1,600,000
Shares issued, value			$ 2,896,000
Private Placement | Elona Kogan, J.D. | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			82,872
Shares issued, value			$ 149,998
Private Placement | Patrick Zenner | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			55,248
Shares issued, value			$ 99,999
Private Placement | Takashi Kei Kishimoto, Ph.D. | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			50,000
Shares issued, value			$ 90,500
Private Placement | Carsten Brunn, Ph.D. | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			41,436
Shares issued, value			$ 74,999
Private Placement | Stephen Smolinski | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			13,812
Shares issued, value			$ 25,000
Warrant | December 2019 Financing | TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.)
Related Party Transaction [Line Items]
Stock issued (in shares)			1,970,443
Warrant | December 2019 Financing | Carrie S. Cox | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			32,840
Warrant | December 2019 Financing | Timothy Barabe | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			32,840
Warrant | December 2019 Financing | Scott D. Myers | Director
Related Party Transaction [Line Items]
Stock issued (in shares)			19,704