| Cover | Nov. 03, 2020 |
| Schedule of Capitalization, Equity [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 3, 2020 |
| Entity File Number | 0-15341 |
| Entity Registrant Name | Donegal Group Inc. |
| Entity Central Index Key | 0000800457 |
| Entity Tax Identification Number | 23-2424711 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1195 River Rd |
| Entity Address, City or Town | Marietta |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 17547 |
| City Area Code | (717) |
| Local Phone Number | 426-1931 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Class A Common Stock, $.01 par value | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | Class A Common Stock, $.01 par value |
| Trading Symbol | DGICA |
| Security Exchange Name | NASDAQ |
| Class B Common Stock, $.01 par value | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | Class B Common Stock, $.01 par value |
| Trading Symbol | DGICB |
| Security Exchange Name | NASDAQ |
