| Document and Entity Information | Dec. 14, 2023 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 14, 2023 |
| Entity Registrant Name | NextCure, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38905 |
| Entity Tax Identification Number | 47-5231247 |
| Entity Address, Address Line One | 9000 Virginia Manor Road |
| Entity Address, Adress Line Two | Suite 200 |
| Entity Address, City or Town | Beltsville |
| Entity Address State Or Province | MD |
| Entity Address, Postal Zip Code | 20705 |
| City Area Code | 240 |
| Local Phone Number | 399-4900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | NXTC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001661059 |
| Amendment Flag | false |
