SEGMENT INFORMATION - Net premiums earned by segment and lines of insurance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenue from External Customer [Line Items]
Premiums earned	$ 133,952	$ 127,189	$ 267,032	$ 247,686
Property and casualty insurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	103,517	97,817	204,764	190,522
Property and casualty insurance [Member] | Commercial Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	91,960	84,994	181,366	164,926
Property and casualty insurance [Member] | Commercial Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	23,855	21,097	46,657	41,221
Property and casualty insurance [Member] | Commercial Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	23,328	21,425	46,645	41,810
Property and casualty insurance [Member] | Commercial Lines [Member] | Workers Compensation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	21,910	21,027	42,963	40,554
Property and casualty insurance [Member] | Commercial Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	21,055	19,602	41,510	37,635
Property and casualty insurance [Member] | Commercial Lines [Member] | Other Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,812	1,843	3,591	3,706
Property and casualty insurance [Member] | Personal Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	11,557	12,823	23,398	25,596
Property and casualty insurance [Member] | Personal Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	6,304	6,917	12,715	13,839
Property and casualty insurance [Member] | Personal Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,062	5,729	10,306	11,416
Property and casualty insurance [Member] | Personal Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	191	177	377	341
Reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	30,435	29,372	62,268	57,164
Reinsurance [Member] | Pro rata reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	11,888	10,305	25,370	20,205
Reinsurance [Member] | Pro rata reinsurance [Member] | Property And Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	3,267	2,483	4,331	3,512
Reinsurance [Member] | Pro rata reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	288	3,645	6,065	8,272
Reinsurance [Member] | Pro rata reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,721	1,125	5,513	1,518
Reinsurance [Member] | Pro rata reinsurance [Member] | Crop Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	775	506	1,213	946
Reinsurance [Member] | Pro rata reinsurance [Member] | Marine And Aviation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	4,837	2,546	8,248	5,957
Reinsurance [Member] | Excess of loss reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	18,547	19,067	36,898	36,959
Reinsurance [Member] | Excess of loss reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	15,800	16,228	31,259	31,449
Reinsurance [Member] | Excess of loss reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,747	2,839	5,638	5,510
Reinsurance [Member] | Excess of loss reinsurance [Member] | Fidelity And Surety Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	$ 0	$ 0	$ 1	$ 0