Product Revenue Net - Summary of Product Revenue Allowance and Reserve Categories (Detail) - TAZVERIK [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 939
Provision	1,798
Payments or credits	(1,592)
Ending Balance	1,145
Chargebacks, Discounts, and Fees [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	244
Provision	558
Payments or credits	(530)
Ending Balance	272
Government and Other Rebates [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	586
Provision	1,245
Payments or credits	(1,062)
Ending Balance	769
Returns [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	109
Provision	5
Payments or credits	0
Ending Balance	$ 104