Statutory Net Income and Surplus (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Statutory Net Income and Surplus
Statutory net income	$ 97,169
Statutory capital and surplus	$ 826,979
Period of statutory measurement of income and dividends	12 months
Maximum available for dividends without approval	$ 97,169
Company's insurance company subsidiaries
Statutory Net Income and Surplus
Statutory net income	97,169	$ 121,446	$ 75,469
Statutory capital and surplus	$ 826,979	$ 754,066
Dividend limitation without prior permission, percentage of preceding surplus	10.00%
Period allowed for Commissioner to object to notice of an extraordinary dividend	30 days
Restricted net assets amount	$ 729,810
Number of levels of regulatory action, risk-based capital law | item	4
Minimum statutory capital and surplus or company action level risk-based capital	$ 200,196
Safety Insurance Company
Statutory Net Income and Surplus
Statutory capital and surplus	826,979
Recorded dividends	$ 49,488