DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) $ in Thousands	Sep. 30, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	$ 1,372,266	$ 1,324,535
Short-term investments	32,798	53,262
Liabilities [Abstract]
Surplus notes	25,000	25,000
Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,177,961	1,127,499
US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,737	9,703
US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	223,465	215,616
US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	343,936	326,058
Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	43,739	46,762
Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	89,684	97,953
Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,738	16,005
Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	448,662	415,402
Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	194,305	197,036
Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,519	34,379
Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,564	26,865
Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,118	26,852
Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	15,769	16,694
Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	19,150	22,691
Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,170	22,863
Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,745	18,221
Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,003	16,056
Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,267	12,415
Recurring [Member]
Assets [Abstract]
Short-term investments	32,798	53,262
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,177,961	1,127,499
Recurring [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,737	9,703
Recurring [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	223,465	215,616
Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	343,936	326,058
Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	43,739	46,762
Recurring [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	89,684	97,953
Recurring [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,738	16,005
Recurring [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	448,662	415,402
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	194,305	197,036
Recurring [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,519	34,379
Recurring [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,564	26,865
Recurring [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,118	26,852
Recurring [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	15,769	16,694
Recurring [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	19,150	22,691
Recurring [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,170	22,863
Recurring [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,745	18,221
Recurring [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,003	16,056
Recurring [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,267	12,415
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	32,798	53,262
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	187,271	192,363
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	34,516	34,376
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	26,564	26,865
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	24,118	26,852
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	15,769	16,694
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	19,150	22,691
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	21,170	22,863
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	17,745	18,221
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	17,003	16,056
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	11,236	7,745
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	1,176,508	1,125,837
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,737	9,703
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	223,465	215,616
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	343,936	326,058
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	43,739	46,762
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	89,684	97,953
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,738	16,005
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	447,209	413,740
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,031	4,670
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	7,031	4,670
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	$ 1,453	$ 1,662
Number of securities categorized as Level 3 fair value measurements | Security	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	1,453	1,662
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 | Security	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	11,269	12,308
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	$ 11,269	$ 12,308