FAIR VALUE (Available-for-Sale Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 443,458	$ 428,641
Equity securities, at fair value	20,824	17,758
Total investments, at fair value	464,282	446,399
United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	145,962	127,868
Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	11,519	9,767
Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	263,385	268,731
International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	22,592	22,275
Level 1
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	43,412	43,918
Equity securities, at fair value	18,907	16,037
Total investments, at fair value	62,319	59,955
Level 1 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	43,412	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:	400,046	384,723
Equity securities, at fair value	1,917	1,721
Total investments, at fair value	401,963	386,444
Level 2 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	102,550	83,950
Level 2 | Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	11,519	9,767
Level 2 | Corporate Securities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	263,385	268,731
Level 2 | International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 22,592	$ 22,275