RESERVES FOR LOSSES AND LOSS SETTLEMENT EXPENSES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross liability for losses and loss settlement expenses at beginning of year	$ 1,224,183	$ 1,123,896	$ 1,003,895
Ceded losses and loss settlement expenses	(59,871)	(59,794)	(54,653)
Net liability for losses and loss settlement expenses at beginning of year	1,164,312	1,064,102	949,242
Losses and loss settlement expenses incurred for claims occurring during
Current year	785,778	779,966	683,662
Prior years	(54,167)	(54,253)	(31,229)
Total incurred	731,611	725,713	652,433
Losses and loss settlement expense payments for claims occurring during
Current year	306,032	311,972	277,053
Prior years	334,502	313,531	260,520
Total paid	640,534	625,503	537,573
Net liability for losses and loss settlement expenses at end of year	1,255,389	1,164,312	1,064,102
Ceded loss and loss settlement expenses	57,094	59,871	59,794
Gross liability for losses and loss settlement expenses at end of year	$ 1,312,483	$ 1,224,183	$ 1,123,896