Statutory Net Income and Surplus (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Statutory Net Income and Surplus
Maximum available for dividends without approval	$ 60,481
Company's insurance company subsidiaries
Statutory Net Income and Surplus
Statutory net income	57,202	$ (12,209)	$ 55,330
Statutory capital and surplus	$ 604,813	$ 571,038
Period of statutory measurement of income and dividends	12 months
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	$ 544,332
Number of levels of regulatory action, risk-based capital law | item	4
Minimum statutory capital and surplus or company action level risk-based capital	$ 107,664
Safety Insurance Company
Statutory Net Income and Surplus
Statutory capital and surplus	604,813
Recorded dividends	$ 39,156