INVESTMENTS - (Summary of Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment Income, Interest and Dividend [Abstract]
Investment Income, Interest	$ 9,776	$ 7,920	$ 6,638
Investment Income, Dividend	478	1,143	588
Net investment income	$ 10,254	$ 9,063	$ 7,226