REINSURANCE - (Premiums Written and Earned) (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premiums Written, Net [Abstract]
Direct											$ 603,417	$ 605,485	$ 493,770
Ceded											(260,524)	(285,986)	(268,516)
Net premiums written											342,893	319,499	225,254
Premiums Earned, Net [Abstract]
Direct											603,193	565,423	432,233
Ceded											(269,712)	(304,054)	(219,213)
Premiums Earned, Net, Property and Casualty	$ 87,503	$ 80,764	$ 83,554	$ 81,660	$ 76,922	$ 69,405	$ 60,045	$ 54,997	$ 165,214	$ 245,978	$ 333,481	$ 261,369	$ 213,020