REINSURANCE (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) reinsurer	Dec. 31, 2015 USD ($) reinsurer	Dec. 31, 2014 USD ($)
Reinsurance Transactions For Insurance Companies, by Product Segment [Line Items]
Number of significant nonaffiliated reinsurers | reinsurer	2	3
Total receivable amount from significant nonaffiliated reinsurers	$ 10,400	$ 12,700
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%
Premiums written
Net premiums written	$ 594,703	$ 578,938	$ 552,610
Premiums earned
Direct	382,300	366,752	372,658
Assumed	637,054	611,045	591,666
Ceded	(426,946)	(407,531)	(423,602)
Net premiums earned	592,408	570,266	540,722
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	386,897	370,736	385,474
Affiliated Entity [Member]
Premiums written
Assumed	491,315	474,323	455,183
Ceded	(396,731)	(381,782)	(378,071)
Premiums earned
Assumed	483,759	466,966	443,440
Ceded	(395,220)	(377,579)	(382,997)
Losses and settlement expenses incurred
Assumed	305,818	295,181	305,857
Ceded	(236,851)	(199,126)	(226,662)
Non Affiliated Entity [Member]
Premiums written
Direct	383,811	370,955	367,732
Assumed	150,780	143,092	147,519
Ceded	(34,472)	(27,650)	(39,753)
Premiums earned
Direct	382,300	366,752	372,658
Assumed	153,295	144,079	148,226
Ceded	(31,726)	(29,952)	(40,605)
Losses and settlement expenses incurred
Direct	229,859	198,504	227,382
Assumed	96,018	85,922	98,482
Ceded	$ (7,947)	$ (9,745)	$ (19,585)
Property and casualty insurance [Member]
Reinsurance Transactions For Insurance Companies, by Product Segment [Line Items]
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%
Premiums written
Net premiums written	$ 463,673	$ 454,434	$ 433,707
Premiums earned
Net premiums earned	456,467	447,197	422,381
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	$ 294,369	$ 291,883	$ 298,033
Property and casualty insurance [Member] | Affiliated Entity [Member]
Reinsurance Transactions For Insurance Companies, by Product Segment [Line Items]
Percentage of pool participation (in hundredths)	30.00%	30.00%	30.00%
Premiums written
Assumed	$ 491,315	$ 474,323	$ 455,183
Ceded	(391,651)	(370,955)	(367,732)
Premiums earned
Assumed	483,759	466,966	443,440
Ceded	(390,140)	(366,752)	(372,658)
Losses and settlement expenses incurred
Assumed	304,007	294,324	304,579
Ceded	(237,318)	(198,504)	(227,382)
Property and casualty insurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	383,811	370,955	367,732
Assumed	4,544	4,392	3,955
Ceded	(24,346)	(24,281)	(25,431)
Premiums earned
Direct	382,300	366,752	372,658
Assumed	4,444	4,240	3,787
Ceded	(23,896)	(24,009)	(24,846)
Losses and settlement expenses incurred
Direct	229,859	198,504	227,382
Assumed	2,712	2,407	2,201
Ceded	(4,891)	(4,848)	(8,747)
Reinsurance [Member]
Premiums written
Net premiums written	131,030	124,504	118,903
Premiums earned
Net premiums earned	135,941	123,069	118,341
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	92,528	78,853	87,441
Reinsurance [Member] | Affiliated Entity [Member]
Premiums written
Assumed	0	0	0
Ceded	(5,080)	(10,827)	(10,339)
Premiums earned
Assumed	0	0	0
Ceded	(5,080)	(10,827)	(10,339)
Losses and settlement expenses incurred
Assumed	1,811	857	1,278
Ceded	467	(622)	720
Reinsurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	0	0	0
Assumed	146,236	138,700	143,564
Ceded	(10,126)	(3,369)	(14,322)
Premiums earned
Direct	0	0	0
Assumed	148,851	139,839	144,439
Ceded	(7,830)	(5,943)	(15,759)
Losses and settlement expenses incurred
Direct	0	0	0
Assumed	93,306	83,515	96,281
Ceded	$ (3,056)	$ (4,897)	$ (10,838)