SEGMENT REPORTING Schedule of Gross Premiums Written by Line of Business (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
Segment Reporting Information [Line Items]
Gross premiums written	$ 138,960	$ 181,588	$ 174,889	$ 197,214	$ 148,838	$ 128,205	$ 92,237	$ 166,792	$ 692,651	$ 536,072	$ 502,124
Gross premiums by line of business as a percentage of total gross premiums									100.00%	100.00%	100.00%
Total Property
Segment Reporting Information [Line Items]
Gross premiums written									$ 141,914	$ 103,624	$ 107,657
Gross premiums by line of business as a percentage of total gross premiums									20.50%	19.30%	21.50%
Commercial
Segment Reporting Information [Line Items]
Gross premiums written									$ 18,388	$ 16,180	$ 15,633
Gross premiums by line of business as a percentage of total gross premiums									2.70%	3.00%	3.10%
Motor
Segment Reporting Information [Line Items]
Gross premiums written									$ 73,481	$ 39,551	$ 34,529
Gross premiums by line of business as a percentage of total gross premiums									10.60%	7.40%	6.90%
Personal
Segment Reporting Information [Line Items]
Gross premiums written									$ 50,045	$ 47,893	$ 57,495
Gross premiums by line of business as a percentage of total gross premiums									7.20%	8.90%	11.50%
Total Casualty
Segment Reporting Information [Line Items]
Gross premiums written									$ 413,939	$ 324,783	$ 309,497
Gross premiums by line of business as a percentage of total gross premiums									59.70%	60.60%	61.70%
General Liability
Segment Reporting Information [Line Items]
Gross premiums written									$ 33,519	$ 34,450	$ 27,620
Gross premiums by line of business as a percentage of total gross premiums									4.80%	6.40%	5.50%
Motor
Segment Reporting Information [Line Items]
Gross premiums written									$ 287,749	$ 227,030	$ 203,624
Gross premiums by line of business as a percentage of total gross premiums									41.50%	42.40%	40.60%
Professional
Segment Reporting Information [Line Items]
Gross premiums written									$ 44,910	$ 37,847	$ 65,607
Gross premiums by line of business as a percentage of total gross premiums									6.50%	7.10%	13.10%
Workers' Compensation
Segment Reporting Information [Line Items]
Gross premiums written									$ 47,761	$ 25,456	$ 12,646
Gross premiums by line of business as a percentage of total gross premiums									6.90%	4.70%	2.50%
Total Specialty [Domain]
Segment Reporting Information [Line Items]
Gross premiums written									$ 136,798	$ 107,665	$ 84,970
Gross premiums by line of business as a percentage of total gross premiums									19.80%	20.10%	16.80%
Accident & Health
Segment Reporting Information [Line Items]
Gross premiums written									$ 69,803	$ 52,114	$ 56,784
Gross premiums by line of business as a percentage of total gross premiums									10.10%	9.70%	11.30%
Financial
Segment Reporting Information [Line Items]
Gross premiums written									$ 48,448	$ 34,658	$ 6,699
Gross premiums by line of business as a percentage of total gross premiums									7.00%	6.50%	1.30%
Marine
Segment Reporting Information [Line Items]
Gross premiums written									$ 6,574	$ 9,127	$ 9,283
Gross premiums by line of business as a percentage of total gross premiums									1.00%	1.70%	1.80%
Other
Segment Reporting Information [Line Items]
Gross premiums written									$ 11,973	$ 11,766	$ 12,204
Gross premiums by line of business as a percentage of total gross premiums									1.70%	2.20%	2.40%