DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Recurring [Member]
Assets [Abstract]
Short-term investments	$ 60,317	$ 56,166
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,030,001	1,027,984
Recurring [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,524	9,412
Recurring [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	147,688	146,946
Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	360,368	357,052
Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	59,357	68,939
Recurring [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	94,112	94,179
Recurring [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	11,525	12,648
Recurring [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	347,427	338,808
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	175,674	169,848
Recurring [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	28,701	28,498
Recurring [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,860	18,917
Recurring [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,280	21,945
Recurring [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	13,662	13,011
Recurring [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,960	21,031
Recurring [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,527	21,117
Recurring [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,593	17,264
Recurring [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	16,919	17,811
Recurring [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	12,172	10,254
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	60,317	56,166
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	171,125	165,386
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	28,698	28,495
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,860	18,917
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,280	21,945
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	13,662	13,011
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,960	21,031
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,527	21,117
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,593	17,264
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	16,919	17,811
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,626	5,795
Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Assets [Abstract]
Short-term investments	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,028,026	1,026,008
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,524	9,412
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	147,688	146,946
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	360,368	357,052
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	59,357	68,939
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	94,112	94,179
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	11,525	12,648
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	345,452	336,832
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	4,546	4,459
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	4,546	4,459
Recurring [Member] | Significant unobservable inputs (Level 3) [Member]
Assets [Abstract]
Short-term investments	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,975	1,976
Number of securities categorized as Level 3 fair value measurements	2	2
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,975	1,976
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	3	3
Number of securities categorized as Level 3 fair value measurements	1	1
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	3	3
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Not Reported At Fair Value [Member]
Liabilities [Abstract]
Surplus notes	10,728	10,040
Not Reported At Fair Value [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Liabilities [Abstract]
Surplus notes	0	0
Not Reported At Fair Value [Member] | Significant other observable inputs (Level 2) [Member]
Liabilities [Abstract]
Surplus notes	0	0
Not Reported At Fair Value [Member] | Significant unobservable inputs (Level 3) [Member]
Liabilities [Abstract]
Surplus notes	$ 10,728	$ 10,040