SEGMENT INFORMATION - Net premiums earned by segment and lines of insurance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue from External Customer [Line Items]
Premiums earned	$ 138,316	$ 132,362	$ 405,348	$ 380,048
Property and casualty insurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	107,952	100,085	312,716	290,607
Property and casualty insurance [Member] | Commercial Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	96,291	87,339	277,657	252,265
Property and casualty insurance [Member] | Commercial Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	25,000	22,254	71,657	63,475
Property and casualty insurance [Member] | Commercial Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	25,111	22,337	71,756	64,147
Property and casualty insurance [Member] | Commercial Lines [Member] | Workers Compensation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	22,209	20,784	65,172	61,338
Property and casualty insurance [Member] | Commercial Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	22,090	20,066	63,600	57,701
Property and casualty insurance [Member] | Commercial Lines [Member] | Other Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,881	1,898	5,472	5,604
Property and casualty insurance [Member] | Personal Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	11,661	12,746	35,059	38,342
Property and casualty insurance [Member] | Personal Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	6,284	6,876	18,999	20,715
Property and casualty insurance [Member] | Personal Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,177	5,688	15,483	17,104
Property and casualty insurance [Member] | Personal Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	200	182	577	523
Reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	30,364	32,277	92,632	89,441
Reinsurance [Member] | Pro rata reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	9,972	13,174	35,342	33,379
Reinsurance [Member] | Pro rata reinsurance [Member] | Property And Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	700	824	5,031	4,336
Reinsurance [Member] | Pro rata reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,198	5,862	7,263	14,134
Reinsurance [Member] | Pro rata reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	3,148	1,432	8,661	2,950
Reinsurance [Member] | Pro rata reinsurance [Member] | Crop Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,400	612	2,613	1,558
Reinsurance [Member] | Pro rata reinsurance [Member] | Marine And Aviation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	3,526	4,444	11,774	10,401
Reinsurance [Member] | Excess of loss reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	20,392	19,103	57,290	56,062
Reinsurance [Member] | Excess of loss reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	17,248	16,509	48,507	47,958
Reinsurance [Member] | Excess of loss reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	3,051	2,594	8,689	8,104
Reinsurance [Member] | Excess of loss reinsurance [Member] | Fidelity And Surety Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	$ 93	$ 0	$ 94	$ 0