License, Collaboration and Research Subaward Agreements - Additional Information (Details)		1 Months Ended			3 Months Ended	12 Months Ended
	Feb. 06, 2018 USD ($) Product	Oct. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	May 31, 2015 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense						$ 0	$ 0
Patent costs as general and administrative expense						7,286,000	1,820,000
Loss from operations						(33,108,000)	(7,586,000)
Grant revenue						2,425,000	2,521,000
Regents of the University of California
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense						25,000	25,000
Upfront license fees paid				$ 500,000
Common stock, shares, issued | shares				107,108
Annual license maintenance fees				$ 25,000
Worldwide sales milestones based on achievement of tiered revenue levels				75,000,000
Patent costs as general and administrative expense						200,000	100,000
Velos Biopharma Holdings, LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of preclinical product candidates licensed and assigned | Product	2
University of California San Diego School of Medicine | The California Institute for Regenerative Medicine ("CIRM") Award
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Grants awarded to researchers		$ 5,800,000	$ 18,300,000
Development milestones to be received under research subaward agreements throughout award project period			$ 14,000,000
Subaward payments received						6,200,000	500,000
Grant revenue						2,400,000	2,500,000
Related qualifying subaward costs						5,400,000	4,600,000
Exclusive License Agreement | Georgetown University
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual license maintenance fee to be paid and payment made									$ 10,000
Potential milestone payments					$ 0	$ 0
Written notice of termination, period						90 days
Days after receipt of notice, to pay failure amount						30 days
Days after receipt of notice for default in payment						60 days
Minimum period in days of written notice to terminate license agreement						60 days
Research and development expense						$ 27,000	53,000
Collaborative Arrangement | MD Anderson Cancer Center
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential regulatory milestone payments										$ 1,000,000
Research Agreement | Regents of the University of California
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense						$ 500,000
Research agreement term						5 years
Aggregate research agreement budget						$ 3,600,000
Research amount payable quarterly						$ 125,000
Regents License Agreement | Velos Biopharma Holdings, LLC | Spin-off Transactions
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of tax free interest distribution								100.00%
Number of preclinical product candidates licensed and assigned | Product	2
Promissory note receivable	$ 100,000
Annual interest rate	2.64%
Promissory note maturity period	10 years
Payment obligations to advance licensed assets	$ 500,000
Research agreement obligation	$ 500,000
Regents License Agreement | Regents of the University of California
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice of termination, period						60 days
SARM License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense						$ 100,000	0
SARD License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense					$ 200,000		0
Asset Purchase Agreement | Velos Biopharma Holdings, LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of preclinical product candidates licensed and assigned | Product	2
Convertible note payable	$ 200,000
Accrued interest of convertible note payable	$ 16,000
Percentage of devoting business activities						80.00%
Loss from operations							$ 3,000,000
Maximum | The California Institute for Regenerative Medicine ("CIRM") Award
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount agreed to be provided in contingency funds		$ 1,000,000
Maximum | Regents of the University of California
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential regulatory milestone payments				12,500,000
Maximum | Exclusive License Agreement | Georgetown University
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments									$ 200,000
Collaborative agreement research funding amount								$ 150,000
Minimum [Member] | Regents of the University of California
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential regulatory milestone payments				10,000,000
Advance licensed assets				$ 1,000,000