| Document And Entity Information - shares | Mar. 31, 2020 | Apr. 27, 2020 |
| Document Information [Line Items] | ||
| Entity, Registrant Name | SERVISFIRST BANCSHARES, INC | |
| Current Fiscal Year End Date | --12-31 | |
| Document, Fiscal Period Focus | Q1 | |
| Document, Fiscal Year Focus | 2020 | |
| Document, Type | 10-Q/A | |
| Document, Quarterly Report | true | |
| Document, Period End Date | Mar. 31, 2020 | |
| Document, Transition Report | false | |
| Entity, File Number | 001-36452 | |
| Entity, Incorporation, State or Country Code | DE | |
| Entity, Tax Identification Number | 26-0734029 | |
| Entity, Address, Address Line One | 2500 Woodcrest Place | |
| Entity, Address, City or Town | Birmingham | |
| Entity, Address, State or Province | AL | |
| Entity, Address, Postal Zip Code | 35209 | |
| City Area Code | 205 | |
| Local Phone Number | 949-0302 | |
| Title of 12(b) Security | Common stock, par value $.001 per share | |
| Trading Symbol | SFBS | |
| Security Exchange Name | NASDAQ | |
| Entity, Current Reporting Status | Yes | |
| Entity, Interactive Data, Current | Yes | |
| Entity, Filer Category | Large Accelerated Filer | |
| Entity, Small Business | false | |
| Entity, Emerging Growth Company | false | |
| Entity, Shell Company | false | |
| Entity, Common Stock Shares, Outstanding | 53,844,009 | |
| Amendment Description | Form 10-Q/A | |
| Amendment Flag | true | |
| Entity, Central Index Key | 0001430723 |
