REINSURANCE (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Premiums written
Net premiums written	$ 158,072	$ 144,875
Premiums earned
Net premiums earned	155,786	144,487
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	110,628	96,285
Affiliated Entity [Member]
Premiums written
Assumed	130,201	124,800
Ceded	(104,337)	(100,944)
Premiums earned
Assumed	129,148	122,097
Ceded	(100,038)	(100,091)
Losses and settlement expenses incurred
Assumed	86,325	77,106
Ceded	(52,001)	(63,343)
Non Affiliated Entity [Member]
Premiums written
Direct	100,044	96,752
Assumed	42,139	34,424
Ceded	(9,975)	(10,157)
Premiums earned
Direct	95,745	95,898
Assumed	42,094	35,704
Ceded	(11,163)	(9,121)
Losses and settlement expenses incurred
Direct	52,287	62,761
Assumed	27,407	21,992
Ceded	$ (3,390)	$ (2,231)
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%
Premiums written
Net premiums written	$ 120,269	$ 114,607
Premiums earned
Net premiums earned	118,632	113,648
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	83,501	75,520
Property and casualty insurance [Member] | Affiliated Entity [Member]
Premiums written
Assumed	130,201	124,800
Ceded	(103,024)	(99,731)
Premiums earned
Assumed	129,148	122,097
Ceded	(98,725)	(98,878)
Losses and settlement expenses incurred
Assumed	85,967	76,742
Ceded	(52,754)	(63,334)
Property and casualty insurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	100,044	96,752
Assumed	1,018	919
Ceded	(7,970)	(8,133)
Premiums earned
Direct	95,745	95,898
Assumed	1,002	1,015
Ceded	(8,538)	(6,484)
Losses and settlement expenses incurred
Direct	52,287	62,761
Assumed	992	752
Ceded	(2,991)	(1,401)
Reinsurance [Member]
Premiums written
Net premiums written	37,803	30,268
Premiums earned
Net premiums earned	37,154	30,839
Losses and settlement expenses incurred
Net losses and settlement expenses incurred	27,127	20,765
Reinsurance [Member] | Affiliated Entity [Member]
Premiums written
Assumed	0	0
Ceded	(1,313)	(1,213)
Premiums earned
Assumed	0	0
Ceded	(1,313)	(1,213)
Losses and settlement expenses incurred
Assumed	358	364
Ceded	753	(9)
Reinsurance [Member] | Non Affiliated Entity [Member]
Premiums written
Direct	0	0
Assumed	41,121	33,505
Ceded	(2,005)	(2,024)
Premiums earned
Direct	0	0
Assumed	41,092	34,689
Ceded	(2,625)	(2,637)
Losses and settlement expenses incurred
Direct	0	0
Assumed	26,415	21,240
Ceded	$ (399)	$ (830)