SEGMENT REPORTING Schedule of Revenue by Major Customers (Details) - USD ($) $ in Thousands	3 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	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Major Customer [Line Items]
Number of operating segments									1
Largest broker	$ 124,535	$ 236,149	$ 121,478	$ 163,513	$ 188,735	$ 145,545	$ 87,810	$ 166,276	$ 645,675	$ 588,366	$ 123,050
Broker Concentration Risk | Gross Premiums Written
Revenue, Major Customer [Line Items]
Largest broker									$ 491,710	$ 379,500	$ 388,249
Concentration risk, percentage									71.00%	70.80%	77.40%
Broker Concentration Risk | Gross Premiums Written | Largest broker
Revenue, Major Customer [Line Items]
Largest broker									$ 366,390	$ 274,816	$ 278,003
Concentration risk, percentage									52.90%	51.30%	55.40%
Broker Concentration Risk | Gross Premiums Written | 2nd largest broker
Revenue, Major Customer [Line Items]
Largest broker									$ 125,320	$ 104,684	$ 110,246
Concentration risk, percentage									18.10%	19.50%	22.00%
Broker Concentration Risk | Gross Premiums Written | 3rd largest broker
Revenue, Major Customer [Line Items]
Largest broker										$ 0	$ 0
Concentration risk, percentage										0.00%	0.00%