DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) $ in Thousands	Jun. 30, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security
Assets [Abstract]
Fixed maturity securities available-for-sale	$ 1,340,066	$ 1,282,909
Equity investments, at fair value	249,507	215,363
Short-term investments	46,857	28,204
Liabilities [Abstract]
Surplus notes	25,000	25,000
Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	1,340,066	1,282,909
U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,270	8,021
U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	320,827	304,479
Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	269,702	283,651
Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	94,304	84,379
Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	194,444	162,137
Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	17,644	20,834
Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	434,875	419,408
Recurring [Member]
Assets [Abstract]
Short-term investments	46,857	28,204
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	1,340,066	1,282,909
Recurring [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,270	8,021
Recurring [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	320,827	304,479
Recurring [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	269,702	283,651
Recurring [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	94,304	84,379
Recurring [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	194,444	162,137
Recurring [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	17,644	20,834
Recurring [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	434,875	419,408
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	249,507	215,363
Recurring [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	51,313	41,839
Recurring [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	41,911	31,581
Recurring [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	29,513	34,571
Recurring [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	17,547	13,180
Recurring [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	29,178	22,765
Recurring [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	14,613	13,372
Recurring [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	21,636	19,389
Recurring [Member] | Other
Assets [Abstract]
Equity investments, at fair value	15,186	14,371
Recurring [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	18,840	16,654
Recurring [Member] | Investment funds [Member]
Assets [Abstract]
Equity investments, at fair value	9,770	7,641
Recurring [Member] | Investments measured at net asset value (NAV)
Assets [Abstract]
Short-term investments	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	9,770	7,641
Recurring [Member] | Investments measured at net asset value (NAV) | Financial services
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Information technology
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Healthcare
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Consumer staples
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Energy
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Industrials
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Other
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Investments measured at net asset value (NAV) | Investment funds [Member]
Assets [Abstract]
Equity investments, at fair value	9,770	7,641
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	46,857	28,204
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	229,956	201,393
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	51,313	41,839
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	41,911	31,581
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	29,513	34,571
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	17,547	13,180
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	29,178	22,765
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	14,613	13,372
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	21,636	19,389
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	15,186	14,371
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	9,059	10,325
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Investment funds [Member]
Assets [Abstract]
Equity investments, at fair value	0	0
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]
Fixed maturity securities available-for-sale	1,339,914	1,282,650
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,270	8,021
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	320,827	304,479
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	269,702	283,651
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	94,304	84,379
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	194,444	162,137
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	17,644	20,834
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	434,723	419,149
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	9,781	6,329
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	9,781	6,329
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Investment funds [Member]
Assets [Abstract]
Equity investments, at fair value	0	0
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]
Fixed maturity securities available-for-sale	$ 152	$ 259
Number of securities categorized as Level 3 fair value measurements | Security	1	2
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	$ 0	$ 0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	152	259
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	$ 0	$ 0
Number of securities categorized as Level 3 fair value measurements | Security	1	1
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	$ 0	$ 0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	0	0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Investment funds [Member]
Assets [Abstract]
Equity investments, at fair value	0	0
Not Reported At Fair Value [Member]
Liabilities [Abstract]
Surplus notes	16,626	15,259
Not Reported At Fair Value [Member] | Investments measured at net asset value (NAV)
Liabilities [Abstract]
Surplus notes	0	0
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	$ 16,626	$ 15,259