| Cover | Jan. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 28, 2021 |
| Entity Registrant Name | CROSSFIRST BANKSHARES, INC. |
| Entity Incorporation, State or Country Code | KS |
| Entity File Number | 001-39028 |
| Entity Tax Identification Number | 26-3212879 |
| Entity Address, Address Line One | 11440 Tomahawk Creek Parkway |
| Entity Address, City or Town | Leawood |
| Entity Address, State or Province | KS |
| Entity Address, Postal Zip Code | 66211 |
| City Area Code | (913) |
| Local Phone Number | 312-6822 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | CFB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001458412 |
| Amendment Flag | false |
