| Document and Entity Information | Nov. 19, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Document Period End Date | Nov. 19, 2020 |
| Entity Registrant Name | Spirit of Texas Bancshares, Inc. |
| Entity Incorporation State Country Code | TX |
| Entity File Number | 001-38484 |
| Entity Tax Identification Number | 90-0499552 |
| Entity Address, Address Line One | 1836 Spirit of Texas Way |
| Entity Address, City or Town | Conroe |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77301 |
| City Area Code | 936 |
| Local Phone Number | 521-1836 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, no par value |
| Trading Symbol | STXB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Amendment Description | Explanatory Note.On February 22, 2021, Spirit of Texas Bancshares, Inc. (the “Company”) entered into a new Executive Employment Agreement with Ms. Allison S. Johnson in connection with her appointment as Executive Vice President and Chief Financial Officer of both the Company and its wholly-owned subsidiary, Spirit of Texas SSB (the “Bank”), effective November 19, 2020 (the “Johnson Employment Agreement”). A copy of the Johnson Employment Agreement was included as Exhibit 10.1 to the Current Report on Form 8-K/A filed by the Company with the Securities and Exchange Commission (the “SEC”) on February 26, 2021 (the “Johnson Form 8-K”).On June 10, 2021, the Company entered into a new Executive Employment Agreement with Mr. Jerry D. Golemon in connection with his position as Executive Vice President and Chief Operations Officer of both the Company and the Bank, effective June 10, 2021 (the “Golemon Employment Agreement” and together with the Johnson Employment Agreement, the “Employment Agreements”). A copy of the Golemon Employment Agreement was included as Exhibit 10.1 to the Current Report on Form 8-K filed by the Company with the SEC on June 16, 2021 (the “Golemon Form 8-K”).The Johnson Form 8-K and Golemon Form 8-K inadvertently attached the incorrect versions of the Employment Agreements. The as-filed Employment Agreements did not reflect the correct severance amount payable to Ms. Johnson and Mr. Golemon in the event such severance were to result from death or disability or were to be without Cause or for Good Reason (as such terms are defined in their respective Employment Agreements) (the “Severance Amount”). Accordingly, this Amendment is being filed to (1) attach the correct versions of the Employment Agreements, and (2) amend and restate the descriptions of the Employment Agreements to reflect the corrected Severance Amount. Other than the change in the Severance Amount, there are no other changes to the Employment Agreements that were filed with the Johnson Form 8-K and Golemon Form 8-K. |
| Amendment Flag | true |
| Entity Central Index Key | 0001499453 |
