SEGMENT INFORMATION - Net premiums earned by segment and lines of insurance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenue from External Customer [Line Items]
Premiums earned	$ 145,788	$ 138,316	$ 429,124	$ 405,348
Property and casualty insurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	113,753	107,952	333,212	312,716
Property and casualty insurance [Member] | Commercial Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	102,864	96,291	300,362	277,657
Property and casualty insurance [Member] | Commercial Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	27,080	25,000	78,698	71,657
Property and casualty insurance [Member] | Commercial Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	26,526	25,111	77,518	71,756
Property and casualty insurance [Member] | Commercial Lines [Member] | Workers Compensation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	23,777	22,209	69,150	65,172
Property and casualty insurance [Member] | Commercial Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	23,449	22,090	68,952	63,600
Property and casualty insurance [Member] | Commercial Lines [Member] | Other Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,032	1,881	6,044	5,472
Property and casualty insurance [Member] | Personal Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	10,889	11,661	32,850	35,059
Property and casualty insurance [Member] | Personal Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,717	6,284	17,313	18,999
Property and casualty insurance [Member] | Personal Lines [Member] | Homeowners Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,172	5,377	15,537	16,060
Reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	32,035	30,364	95,912	92,632
Reinsurance [Member] | Pro rata reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	13,037	9,972	40,154	35,342
Reinsurance [Member] | Pro rata reinsurance [Member] | Multiline (primarily property) Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,190	700	4,584	5,031
Reinsurance [Member] | Pro rata reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	4,162	2,622	11,877	9,929
Reinsurance [Member] | Pro rata reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	4,787	3,148	13,955	8,661
Reinsurance [Member] | Pro rata reinsurance [Member] | Marine Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,898	3,502	9,738	11,721
Reinsurance [Member] | Excess of loss reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	18,998	20,392	55,758	57,290
Reinsurance [Member] | Excess of loss reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	16,249	17,248	46,425	48,507
Reinsurance [Member] | Excess of loss reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	$ 2,749	$ 3,144	$ 9,333	$ 8,783