DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS, Recurring Measurement Inputs (Details) $ in Thousands	Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($) Security
Assets [Abstract]
Fixed maturity securities available-for-sale	$ 1,282,909	$ 1,275,016
Equity investments, at fair value	215,363
Equity securities available-for-sale		228,115
Short-term investments	28,204	23,613
Liabilities [Abstract]
Surplus notes	25,000	25,000
Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	1,282,909	1,275,016
U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,021	8,078
U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	304,479	297,949
Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	283,651	307,536
Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	84,379	83,980
Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	162,137	119,799
Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	20,834	24,114
Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	419,408	433,560
Equity Securities [Member]
Assets [Abstract]
Equity securities available-for-sale		228,115
Financial services
Assets [Abstract]
Equity securities available-for-sale		43,522
Information technology
Assets [Abstract]
Equity securities available-for-sale		35,810
Healthcare
Assets [Abstract]
Equity securities available-for-sale		30,595
Consumer staples
Assets [Abstract]
Equity securities available-for-sale		14,127
Consumer discretionary
Assets [Abstract]
Equity securities available-for-sale		20,538
Energy
Assets [Abstract]
Equity securities available-for-sale		16,905
Industrials
Assets [Abstract]
Equity securities available-for-sale		28,489
Other
Assets [Abstract]
Equity securities available-for-sale		16,421
Non-redeemable preferred stocks
Assets [Abstract]
Equity securities available-for-sale		21,708
Recurring [Member]
Assets [Abstract]
Short-term investments	28,204	23,613
Recurring [Member] | Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	1,282,909	1,275,016
Recurring [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,021	8,078
Recurring [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	304,479	297,949
Recurring [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	283,651	307,536
Recurring [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	84,379	83,980
Recurring [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	162,137	119,799
Recurring [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	20,834	24,114
Recurring [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	419,408	433,560
Recurring [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	215,363
Equity securities available-for-sale		228,115
Recurring [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	41,839
Equity securities available-for-sale		43,522
Recurring [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	31,581
Equity securities available-for-sale		35,810
Recurring [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	34,571
Equity securities available-for-sale		30,595
Recurring [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	13,180
Equity securities available-for-sale		14,127
Recurring [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	22,765
Equity securities available-for-sale		20,538
Recurring [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	13,372
Equity securities available-for-sale		16,905
Recurring [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	19,389
Equity securities available-for-sale		28,489
Recurring [Member] | Other
Assets [Abstract]
Equity investments, at fair value	14,371
Equity securities available-for-sale		16,421
Recurring [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	16,654
Equity securities available-for-sale		21,708
Recurring [Member] | Investment funds
Assets [Abstract]
Equity investments, at fair value	7,641
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Assets [Abstract]
Short-term investments	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Debt Securities [Member]
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	0	0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	7,641
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Financial services
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Information technology
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Healthcare
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Consumer staples
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Consumer discretionary
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Energy
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Industrials
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Other
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity securities available-for-sale		0
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets [Abstract]
Short-term investments	28,204	23,613
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	201,393
Equity securities available-for-sale		215,916
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	41,839
Equity securities available-for-sale		43,519
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	31,581
Equity securities available-for-sale		35,810
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	34,571
Equity securities available-for-sale		30,595
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	13,180
Equity securities available-for-sale		14,127
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	22,765
Equity securities available-for-sale		20,538
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	13,372
Equity securities available-for-sale		16,905
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	19,389
Equity securities available-for-sale		28,489
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	14,371
Equity securities available-for-sale		16,421
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	10,325
Equity securities available-for-sale		9,512
Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Investment funds
Assets [Abstract]
Equity investments, at fair value	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	1,282,650	1,274,396
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. treasury
Assets [Abstract]
Fixed maturity securities available-for-sale	8,021	8,078
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. government-sponsored agencies
Assets [Abstract]
Fixed maturity securities available-for-sale	304,479	297,949
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Obligations of states and political subdivisions
Assets [Abstract]
Fixed maturity securities available-for-sale	283,651	307,536
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Commercial mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	84,379	83,980
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	162,137	119,799
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other asset-backed
Assets [Abstract]
Fixed maturity securities available-for-sale	20,834	24,114
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate
Assets [Abstract]
Fixed maturity securities available-for-sale	419,149	432,940
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	6,329
Equity securities available-for-sale		10,196
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	6,329
Equity securities available-for-sale		10,196
Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Investment funds
Assets [Abstract]
Equity investments, at fair value	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	$ 259	$ 620
Number of securities categorized as Level 3 fair value measurements | Security	2	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	259	620
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity Securities [Member]
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		$ 2,003
Number of securities categorized as Level 3 fair value measurements | Security		2
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Financial services
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		$ 3
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Information technology
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Healthcare
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Consumer staples
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Consumer discretionary
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Energy
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Industrials
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		0
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Non-redeemable preferred stocks
Assets [Abstract]
Equity investments, at fair value	0
Equity securities available-for-sale		2,000
Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Investment funds
Assets [Abstract]
Equity investments, at fair value	0
Not Reported At Fair Value [Member]
Liabilities [Abstract]
Surplus notes	15,259	16,689
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	15,259	16,689
Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Liabilities [Abstract]
Surplus notes	$ 0	$ 0