FAIR VALUE (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 425,489	$ 423,238
Equity securities, at fair value	17,383	15,434
Total investments, at fair value	442,872	438,672
United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	107,227	98,137
Total investments, at fair value	107,227	98,137
Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	24,041	66,266
Total investments, at fair value	24,041	66,266
Corporate Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	274,881	240,919
Total investments, at fair value	274,881	240,919
International Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	19,340	17,916
Total investments, at fair value	19,340	17,916
Level 1 [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	56,378	51,219
Equity securities, at fair value	17,383	15,434
Total investments, at fair value	73,761	66,653
Level 1 [Member] | United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	56,378	51,219
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 1 [Member] | Corporate Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 1 [Member] | International Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	0
Level 2 [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	369,111	372,019
Equity securities, at fair value		0
Total investments, at fair value	369,111	372,019
Level 2 [Member] | United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	50,849	46,918
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	24,041	66,266
Level 2 [Member] | Corporate Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	274,881	240,919
Level 2 [Member] | International Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 19,340	$ 17,916