FAIR VALUE (Available-for-Sale Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 451,124	$ 428,641
Equity securities, at fair value	22,112	17,758
Total investments, at fair value	473,236	446,399
United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	150,720	127,868
Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	11,717	9,767
Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	267,994	268,731
International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	20,693	22,275
Level 1
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	50,047	43,918
Equity securities, at fair value	20,114	16,037
Total investments, at fair value	70,161	59,955
Level 1 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	50,047	43,918
Level 1 | Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 1 | Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 1 | International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 2
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	401,077	384,723
Equity securities, at fair value	1,998	1,721
Total investments, at fair value	403,075	386,444
Level 2 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	100,673	83,950
Level 2 | Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	11,717	9,767
Level 2 | Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	267,994	268,731
Level 2 | International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 20,693	$ 22,275