LIABILITY FOR LOSSES AND SETTLEMENT EXPENSES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of beginning and ending reserves for losses and settlement expenses [Roll Forward]
Gross reserves at beginning of year	$ 690,532	$ 678,774	$ 661,309
Re-valuation due to foreign currency exchange rates	(1,913)	(2,475)	(2,061)
Less ceded reserves at beginning of year	20,664	23,477	28,253
Net reserves at beginning of year	671,781	657,772	635,117
Incurred losses and settlement expenses related to:
Current year	441,588	427,838	405,850
Prior years	(19,619)	(40,941)	(35,114)
Total incurred losses and settlement expenses	421,969	386,897	370,736
Paid losses and settlement expenses related to:
Current year	179,354	172,652	154,958
Prior years	213,232	200,236	193,123
Total paid losses and settlement expenses	392,586	372,888	348,081
Net reserves at end of year	701,164	671,781	657,772
Plus ceded reserves at end of year	30,923	20,664	23,477
Re-valuation due to foreign currency exchange rates	525	(1,913)	(2,475)
Gross reserves at end of year	$ 732,612	$ 690,532	$ 678,774
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%
Property and casualty insurance [Member]
Incurred losses and settlement expenses related to:
Prior years	$ (15,700)	$ (30,000)	$ (13,800)
Percentage change in loss and settlement expense reserves for prior accident years (in hundredths)	(3.20%)	(5.10%)	(2.90%)
Paid losses and settlement expenses related to:
Adjustment for favorable (adverse) development included in the reported development amount that had no impact on earnings		$ 5,600	$ 400
Approximation of the implied amount of favorable development that had an impact on earnings		$ 24,400	$ 13,400
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%
Reinsurance [Member]
Incurred losses and settlement expenses related to:
Prior years	$ (3,900)	$ (10,900)	$ (21,300)
Percentage change in loss and settlement expense reserves for prior accident years (in hundredths)	(1.90%)	(5.50%)	(11.30%)
Paid losses and settlement expenses related to:
Adjustment for favorable (adverse) development included in the reported development amount that had no impact on earnings			$ (1,000)
Approximation of the implied amount of favorable development that had an impact on earnings			$ 22,300
Affiliated Entity [Member] | Property and casualty insurance [Member]
Paid losses and settlement expenses related to:
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%