FAIR VALUE (Available-for-Sale Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 468,130	$ 428,641
Equity securities, at fair value	19,014	17,758
Total investments, at fair value	487,144	446,399
United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	174,240	127,868
Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	13,328	9,767
Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	255,399	268,731
International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	25,163	22,275
Level 1
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	73,590	43,918
Equity securities, at fair value	16,570	16,037
Total investments, at fair value	90,160	59,955
Level 1 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	73,590	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:	394,540	384,723
Equity securities, at fair value	2,444	1,721
Total investments, at fair value	396,984	386,444
Level 2 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	100,650	83,950
Level 2 | Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	13,328	9,767
Level 2 | Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	255,399	268,731
Level 2 | International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 25,163	$ 22,275