DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) $ in Thousands	Mar. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	$ 1,378,604	$ 1,367,268
Short-term investments	48,447	38,599
Liabilities [Abstract]
Surplus notes	25,000	25,000
Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,166,022	1,161,025
US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	8,138	12,589
US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	189,448	202,666
US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	340,780	344,359
Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	41,757	46,108
Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	88,122	88,543
Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	16,644	17,844
Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	481,133	448,916
Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	212,582	206,243
Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	33,443	33,955
Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	28,519	28,102
Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,440	25,894
Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	19,581	18,200
Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,037	18,923
Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,590	21,068
Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,521	20,416
Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,492	20,683
Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,959	19,002
Recurring [Member]
Assets [Abstract]
Short-term investments	48,447	38,599
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,166,022	1,161,025
Recurring [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	8,138	12,589
Recurring [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	189,448	202,666
Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	340,780	344,359
Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	41,757	46,108
Recurring [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	88,122	88,543
Recurring [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	16,644	17,844
Recurring [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	481,133	448,916
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	212,582	206,243
Recurring [Member] | Common stocks Financial services [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	33,443	33,955
Recurring [Member] | Common stocks Information technology [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	28,519	28,102
Recurring [Member] | Common stocks Healthcare [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,440	25,894
Recurring [Member] | Common stocks Consumer staples [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	19,581	18,200
Recurring [Member] | Common stocks Consumer discretionary [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,037	18,923
Recurring [Member] | Common stocks Energy [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	20,590	21,068
Recurring [Member] | Common stocks Industrials [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,521	20,416
Recurring [Member] | Common stocks Other [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,492	20,683
Recurring [Member] | Nonredeemable Preferred Stock [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	18,959	19,002
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	48,447	38,599
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	205,198	198,944
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	33,440	33,952
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	28,519	28,102
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	24,440	25,894
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	19,581	18,200
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	22,037	18,923
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	20,590	21,068
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	23,521	20,416
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	21,492	20,683
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	11,578	11,706
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	1,164,751	1,159,696
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US Treasury Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	8,138	12,589
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	189,448	202,666
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	340,780	344,359
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	41,757	46,108
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential Mortgage Backed Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	88,122	88,543
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Collateralized Debt Obligations [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	16,644	17,844
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	479,862	447,587
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,381	7,296
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	7,381	7,296
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	$ 1,271	$ 1,329
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	1,271	1,329
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	11,071	10,823
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	$ 11,071	$ 10,823