TRANSACTIONS WITH AFFILIATES (Details) - Affiliated Entity [Member] $ in Thousands	3 Months Ended		6 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) Plan	Jun. 30, 2018 USD ($) Plan	Dec. 31, 2017 USD ($) Plan	Jun. 30, 2017 USD ($) Plan	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) Plan	Dec. 31, 2017 USD ($) Plan
Related Party Transaction [Line Items]
Ceded premiums earned	$ 102,852	$ 98,449					$ 306,193	$ 298,108
Ceded losses and settlement expenses incurred	52,070	75,248					166,748	227,404
Property and casualty insurance [Member]
Related Party Transaction [Line Items]
Number of reinsurance program treaties | Plan			1	1	1	1			2	2
Ceded premiums earned	101,540	97,237					302,256	294,471
Ceded losses and settlement expenses incurred	53,997	66,279					169,137	218,425
Property and casualty insurance [Member] | Annual Aggregate Catastrophe Excess of Loss [Member]
Related Party Transaction [Line Items]
Catastrophe claims, retention amount			$ 15,000	$ 22,000	$ 15,000	$ 20,000
Affiliated reinsurance contract first layer limit			12,000	24,000	12,000	24,000
Ceded premiums earned			$ 1,400	$ 6,000	$ 1,400	$ 6,000
Ceded losses and settlement expenses incurred	2,391	3,534					3,175	20,108
Reinsurance [Member]
Related Party Transaction [Line Items]
Number of reinsurance program treaties | Plan									2	2
Ceded premiums earned	1,312	1,212					3,937	3,637
Ceded losses and settlement expenses incurred	$ (1,927)	$ 8,969					$ (2,389)	$ 8,979
Reinsurance [Member] | Per Occurrence Catastrophe Excess of Loss [Member]
Related Party Transaction [Line Items]
Catastrophe claims, retention amount									$ 10,000	$ 10,000
Affiliated reinsurance contract first layer limit									$ 10,000	$ 10,000
First layer excess of loss coinsurance percentage (in hundreths)									20.00%	20.00%
Ceded premiums earned									$ 1,600	$ 1,700
Reinsurance [Member] | Annual Aggregate Catastrophe Excess of Loss [Member]
Related Party Transaction [Line Items]
Catastrophe claims, retention amount									20,000	20,000
Affiliated reinsurance contract first layer limit									$ 100,000	$ 100,000
First layer excess of loss coinsurance percentage (in hundreths)									20.00%	20.00%
Ceded premiums earned									$ 3,600	$ 3,200
Catastrophe event minimum amount									$ 500	$ 500