Debt - Additional Information (Detail) - Credit Facility [Member] - USD ($)		3 Months Ended		6 Months Ended
	Jun. 11, 2025	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Jul. 31, 2025
Debt Instrument [Line Items]
Term loan facility, principal amount	$ 400,000,000
Amount available for borrowing		$ 0		$ 0		$ 25,000,000
Credit facility maturity date	Jun. 01, 2030
Annual interest rate	4.75%
Credit facility, basis spread rate	4.15%
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) [Member]
Line of Credit Facility, Frequency of Payment and Payment Terms	The Company is obligated to make monthly interest-only payments with respect to the Credit Facility until June 1, 2028; however, if certain conditions are satisfied, then the Company may elect to defer principal payments until June 1, 2029. Thereafter, the Company shall make (i) monthly payments of interest plus (ii) consecutive equal monthly payments of principal through to the Maturity Date.
Line of Credit Facility, Frequency of Payments	monthly
Effective interest rate		12.96%		12.96%
Interest expense related to the Credit Facility		$ 300,000	$ 0	$ 300,000	$ 0
Maximum [Member]
Debt Instrument [Line Items]
Prepayment premium rate	3.00%
Minimum [Member]
Debt Instrument [Line Items]
Prepayment premium rate	1.00%
Debt Instrument Tranche One [Member]
Debt Instrument [Line Items]
Term loan facility amount available for use	$ 50,000,000
Debt Instrument Tranche Two [Member]
Debt Instrument [Line Items]
Term loan facility amount available for use	25,000,000
Debt Instrument Tranche Three [Member]
Debt Instrument [Line Items]
Term loan facility amount available for use	75,000,000
Debt Instrument Tranche Four [Member]
Debt Instrument [Line Items]
Term loan facility amount available for use	50,000,000
Net product revenue amount to be achieved to avail tranche four debt amount	85,000,000
Debt Instrument Tranche Five [Member]
Debt Instrument [Line Items]
Term loan facility amount available for use	$ 200,000,000

Cogent Biosciences, Inc. 10-Q