DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) $ in Thousands	Jun. 30, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	$ 1,354,248	$ 1,324,535
Short-term investments	32,758	53,262
Liabilities [Abstract]
Surplus notes	25,000	25,000
Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,154,962	1,127,499
US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,638	9,703
US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	225,312	215,616
US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	327,393	326,058
Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	45,156	46,762
Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	92,249	97,953
Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,599	16,005
Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	440,615	415,402
Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	199,286	197,036
Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	36,289	34,379
Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,836	26,865
Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,271	26,852
Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,335	16,694
Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,732	22,691
Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,893	22,863
Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,293	18,221
Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	12,793	16,056
Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,844	12,415
Recurring [Member]
Assets [Abstract]
Short-term investments	32,758	53,262
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,154,962	1,127,499
Recurring [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	9,638	9,703
Recurring [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	225,312	215,616
Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	327,393	326,058
Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	45,156	46,762
Recurring [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	92,249	97,953
Recurring [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,599	16,005
Recurring [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	440,615	415,402
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	199,286	197,036
Recurring [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	36,289	34,379
Recurring [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,836	26,865
Recurring [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	26,271	26,852
Recurring [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,335	16,694
Recurring [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,732	22,691
Recurring [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,893	22,863
Recurring [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,293	18,221
Recurring [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	12,793	16,056
Recurring [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,844	12,415
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	32,758	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	192,193	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	36,286	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	26,836	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	26,271	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	14,335	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	24,732	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	22,893	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	20,293	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	12,793	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	7,754	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	1,153,340	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	9,638	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	225,312	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	327,393	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	45,156	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	92,249	97,953
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	14,599	16,005
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	438,993	413,740
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,090	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	7,090	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	$ 1,622	$ 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	1,622	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	11,064	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	$ 11,064	$ 12,308