v3.26.1
Cover
Jul. 23, 2026
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Jul. 23, 2026
Entity File Number 000-50070
Entity Registrant Name SAFETY INSURANCE GROUP, INC.
Entity Central Index Key 0001172052
Entity Tax Identification Number 13-4181699
Entity Incorporation, State or Country Code DE
Entity Address, Address Line One 20 Custom House Street
Entity Address, City or Town Boston
Entity Address, State or Province MA
Entity Address, Postal Zip Code 02110
City Area Code 617
Local Phone Number 951-0600
Written Communications false
Soliciting Material true
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock, $0.01 par value per share
Trading Symbol SAFT
Security Exchange Name NASDAQ
Entity Emerging Growth Company false