Related Party Transactions - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Aug. 30, 2021	Oct. 03, 2016	Jan. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Related party transaction, amount paid							$ 135,000	$ 0
Payable to related party				$ 22,000	$ 14,314,000		22,000
Celgene License Agreement [Member]
Related Party Transaction [Line Items]
License agreement option to extension payment		$ 3,000,000.0
Payments related to milestone				0		$ 0	0	0
Payments related to royalties				0		$ 0	0	$ 0
Licensed drug manufacturing costs									$ 2,700,000	$ 1,200,000
Related party transaction, amount paid	$ 5,800,000
Related party transaction, percentage of outstanding payment obligation	50.00%
Payable to related party	$ 5,800,000
Related party transaction, balloon payment interest rate per annum	4.00%
Celgene License Agreement [Member] | EOC Pharma (Hong Kong) Limited [Member]
Related Party Transaction [Line Items]
Related party transaction, amount paid				$ 2,800,000			$ 2,800,000
Payable to related party					2,800,000
Payment received from license agreement			$ 14,000,000.0
Sublicense fees, percentage			20.00%
License expense, related party					$ 2,800,000