FAIR VALUE (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 429,457	$ 423,238
Equity securities, at fair value	16,515	15,434
Total investments, at fair value	445,972	438,672
United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	129,710	98,137
Total investments, at fair value	129,710	98,137
Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	23,302	66,266
Total investments, at fair value	23,302	66,266
Corporate Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	258,518	240,919
Total investments, at fair value	258,518	240,919
International Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	17,927	17,916
Total investments, at fair value	17,927	17,916
Level 1 [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	77,109	51,219
Equity securities, at fair value	16,515	15,434
Total investments, at fair value	93,624	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:	77,109	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:	352,348	372,019
Equity securities, at fair value		0
Total investments, at fair value	352,348	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:	52,601	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:	23,302	66,266
Level 2 [Member] | Corporate Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	258,518	240,919
Level 2 [Member] | International Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 17,927	$ 17,916