REINSURANCE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Premiums written
Net premiums written	$ 163,112	$ 155,145	$ 321,184	$ 300,020
Premiums earned
Net premiums earned	157,946	149,837	313,732	294,324
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	119,091	107,228	229,719	203,513
Affiliated Entity [Member]
Premiums written
Assumed	140,850	136,726	271,051	261,526
Ceded	(102,871)	(97,585)	(207,208)	(198,529)
Premiums earned
Assumed	131,768	125,179	260,916	247,276
Ceded	(103,303)	(99,568)	(203,341)	(199,659)
Losses and settlement expenses incurred
Assumed	95,952	100,681	182,277	177,787
Ceded	(62,677)	(88,813)	(114,678)	(152,156)
Non Affiliated Entity [Member]
Premiums written
Direct	98,579	93,392	198,623	190,144
Assumed	40,516	36,886	82,655	71,310
Ceded	(13,962)	(14,274)	(23,937)	(24,431)
Premiums earned
Direct	99,011	95,376	194,756	191,274
Assumed	41,657	38,541	83,751	74,245
Ceded	(11,187)	(9,691)	(22,350)	(18,812)
Losses and settlement expenses incurred
Direct	62,069	72,811	114,356	135,572
Assumed	27,823	26,870	55,230	48,862
Ceded	$ (4,076)	$ (4,321)	$ (7,466)	$ (6,552)
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%	30.00%
Premiums written
Net premiums written	$ 131,201	$ 126,591	$ 251,470	$ 241,198
Premiums earned
Net premiums earned	121,495	116,187	240,127	229,835
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	94,255	81,508	177,756	157,028
Property and casualty insurance [Member] | Affiliated Entity [Member]
Premiums written
Assumed	140,850	136,726	271,051	261,526
Ceded	(101,559)	(96,373)	(204,583)	(196,104)
Premiums earned
Assumed	131,768	125,179	260,916	247,276
Ceded	(101,991)	(98,356)	(200,716)	(197,234)
Losses and settlement expenses incurred
Assumed	95,713	100,380	181,680	177,122
Ceded	(62,386)	(88,812)	(115,140)	(152,146)
Property and casualty insurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	98,579	93,392	198,623	190,144
Assumed	1,284	1,290	2,302	2,209
Ceded	(7,953)	(8,444)	(15,923)	(16,577)
Premiums earned
Direct	99,011	95,376	194,756	191,274
Assumed	1,300	1,130	2,302	2,145
Ceded	(8,593)	(7,142)	(17,131)	(13,626)
Losses and settlement expenses incurred
Direct	62,069	72,811	114,356	135,572
Assumed	770	693	1,762	1,445
Ceded	(1,911)	(3,564)	(4,902)	(4,965)
Reinsurance [Member]
Premiums written
Net premiums written	31,911	28,554	69,714	58,822
Premiums earned
Net premiums earned	36,451	33,650	73,605	64,489
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	24,836	25,720	51,963	46,485
Reinsurance [Member] | Affiliated Entity [Member]
Premiums written
Assumed	0	0	0	0
Ceded	(1,312)	(1,212)	(2,625)	(2,425)
Premiums earned
Assumed	0	0	0	0
Ceded	(1,312)	(1,212)	(2,625)	(2,425)
Losses and settlement expenses incurred
Assumed	239	301	597	665
Ceded	(291)	(1)	462	(10)
Reinsurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	0	0	0	0
Assumed	39,232	35,596	80,353	69,101
Ceded	(6,009)	(5,830)	(8,014)	(7,854)
Premiums earned
Direct	0	0	0	0
Assumed	40,357	37,411	81,449	72,100
Ceded	(2,594)	(2,549)	(5,219)	(5,186)
Losses and settlement expenses incurred
Direct	0	0	0	0
Assumed	27,053	26,177	53,468	47,417
Ceded	$ (2,165)	$ (757)	$ (2,564)	$ (1,587)