TRANSACTIONS WITH AFFILIATES (Details) - Affiliated Entity [Member] $ in Thousands	3 Months Ended		6 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) Plan	Jun. 30, 2017 USD ($) Plan	Dec. 31, 2016 USD ($) Plan	Jun. 30, 2016 USD ($) Plan	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) Plan	Dec. 31, 2016 USD ($) Plan
Property and casualty insurance [Member]
Related Party Transaction [Line Items]
Number of reinsurance program treaties | Plan			1	1	1	1			2	2
Property and casualty insurance [Member] | Annual Aggregate Catastrophe Excess of Loss [Member]
Related Party Transaction [Line Items]
Catastrophe claims, retention amount			$ 15,000	$ 20,000	$ 15,000	$ 20,000
Affiliated reinsurance contract first layer limit			12,000	24,000	12,000	24,000
Dollar amount of cost of affiliated reinsurance contract			$ 1,400	$ 6,000	$ 1,500	$ 6,300
Ceded losses and settlement expenses incurred	$ 3,000	$ 3,500					$ 19,000	$ 5,100
Reinsurance [Member]
Related Party Transaction [Line Items]
Number of reinsurance program treaties | Plan									2	2
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%
Dollar amount of cost of affiliated reinsurance contract									$ 1,700	$ 2,000
Ceded losses and settlement expenses incurred	0	0					0	0
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%
Dollar amount of cost of affiliated reinsurance contract									$ 3,200	$ 3,200
Catastrophe event minimum amount									$ 500	$ 500
Ceded losses and settlement expenses incurred	$ 9,000	$ 0					$ 9,000	$ 0