INVESTMENTS - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net investment income
Gross investment income									$ 59,482	$ 60,726	$ 57,758
Less investment expenses									(4,838)	(5,118)	(4,995)
Net Investment Income	$ 13,754	$ 13,964	$ 13,431	$ 13,495	$ 13,844	$ 14,200	$ 13,982	$ 13,582	54,644	55,608	52,763
Debt securities
Net investment income
Gross investment income									48,064	48,757	45,870
Equity securities
Net investment income
Gross investment income									11,407	11,962	11,865
Cash and Short-term Investments
Net investment income
Gross investment income									$ 11	$ 7	$ 23