| Cover Cover | Jul. 29, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 29, 2020 |
| Entity Registrant Name | Independent Bank Group, Inc. |
| Entity Incorporation, State or Country Code | TX |
| Entity File Number | 001-35854 |
| Entity Tax Identification Number | 13-4219346 |
| Entity Address, Address Line One | 7777 Henneman Way |
| Entity Address, City or Town | McKinney |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 75070-1711 |
| City Area Code | 972 |
| Local Phone Number | 562-9004 |
| 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 | IBTX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001564618 |
| Amendment Flag | false |
