SCHEDULE IV - REINSURANCE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Gross Amount	$ 1,059,973	$ 1,058,545	$ 997,892
Ceded to Other Companies	125,735	133,981	102,848
Assumed From Other Companies	509	662	1,178
Net Amount	$ 934,747	$ 925,226	$ 896,222
Percentage of Amount Assumed to Net	0.10%	0.10%	0.10%