SEGMENT INFORMATION - Net premiums earned by segment and lines of insurance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenue from External Customer [Line Items]
Premiums earned	$ 133,080	$ 120,497
Property and casualty insurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	101,247	92,705
Property and casualty insurance [Member] | Commercial Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	89,406	79,932
Property and casualty insurance [Member] | Commercial Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	22,802	20,124
Property and casualty insurance [Member] | Commercial Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	23,317	20,385
Property and casualty insurance [Member] | Commercial Lines [Member] | Workers Compensation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	21,053	19,527
Property and casualty insurance [Member] | Commercial Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	20,455	18,033
Property and casualty insurance [Member] | Commercial Lines [Member] | Other Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,779	1,863
Property and casualty insurance [Member] | Personal Lines [Member]
Revenue from External Customer [Line Items]
Premiums earned	11,841	12,773
Property and casualty insurance [Member] | Personal Lines [Member] | Automobile Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	6,411	6,922
Property and casualty insurance [Member] | Personal Lines [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,244	5,687
Property and casualty insurance [Member] | Personal Lines [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	186	164
Reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	31,833	27,792
Reinsurance [Member] | Pro rata reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	13,482	9,900
Reinsurance [Member] | Pro rata reinsurance [Member] | Property And Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	1,064	1,029
Reinsurance [Member] | Pro rata reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	5,777	4,627
Reinsurance [Member] | Pro rata reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,792	393
Reinsurance [Member] | Pro rata reinsurance [Member] | Crop Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	438	440
Reinsurance [Member] | Pro rata reinsurance [Member] | Marine and Aviation Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	3,411	3,411
Reinsurance [Member] | Excess of loss reinsurance [Member]
Revenue from External Customer [Line Items]
Premiums earned	18,351	17,892
Reinsurance [Member] | Excess of loss reinsurance [Member] | Property Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	15,459	15,221
Reinsurance [Member] | Excess of loss reinsurance [Member] | Liability Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	2,891	2,671
Reinsurance [Member] | Excess of loss reinsurance [Member] | Fidelity And Surety Insurance L O B [Member]
Revenue from External Customer [Line Items]
Premiums earned	$ 1	$ 0