Reverse Recapitalization - Narrative (Details) - USD ($) $ in Thousands			6 Months Ended
	Sep. 29, 2023	Sep. 28, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Schedule Of Reverse Recapitalization [Line Items]
Converted shares (in shares)		5,579,266
Stock converted, reverse recapitalization (in shares)	2,278,598
Common stock, shares outstanding (in shares)	21,888,976		25,771,132		21,888,976
Common stock, shares issued (in shares)			25,771,132		21,888,976
Stock options cancelled and converted (in shares)	2,101,760
Reverse recapitalization, transaction costs	$ 7,500
Payments of reverse recapitalization transaction costs			$ 40	$ 1,742
Reverse recapitalization obligation, cash settlement	700
Reverse recapitalization obligation, shares issuable	2,000
Vendor
Schedule Of Reverse Recapitalization [Line Items]
Transaction costs, incurred but not yet paid	2,700
Payments of reverse recapitalization transaction costs	$ 1,300
Legacy NKGen
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)	38,185,814
Common stock, shares issued (in shares)	38,185,814
Options, issued and outstanding (in shares)	5,146,354
Graf Acquisition Partners IV LLC | Vendor
Schedule Of Reverse Recapitalization [Line Items]
Transaction costs, incurred but not yet paid	$ 4,000
Graf Acquisition Partners IV LLC | Vendor | Cash
Schedule Of Reverse Recapitalization [Line Items]
Transaction costs, incurred but not yet paid	2,000
Graf Acquisition Partners IV LLC | Vendor | Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Transaction costs, incurred but not yet paid	2,000
Equity Instruments
Schedule Of Reverse Recapitalization [Line Items]
Reverse recapitalization, transaction costs	4,200
Liability Instruments
Schedule Of Reverse Recapitalization [Line Items]
Reverse recapitalization, transaction costs	$ 3,300
Common Stock, Including Convertible Debt Stock
Schedule Of Reverse Recapitalization [Line Items]
Stock converted, reverse recapitalization (in shares)	15,595,260