FAIR VALUE (Available-for-Sale Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 542,835	$ 526,265
Equity securities, at fair value	17,324	20,039
Total investments, at fair value	560,159	546,304
United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	196,363	194,193
Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	22,298	24,020
Corporate
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	293,730	278,302
International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	30,444	29,750
Level 1
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	66,033	83,764
Equity securities, at fair value	13,720	17,361
Total investments, at fair value	79,753	101,125
Level 1 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	66,033	83,764
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
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:	476,802	442,501
Equity securities, at fair value	3,604	2,678
Total investments, at fair value	480,406	445,179
Level 2 | United States Government Obligations and Authorities
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	130,330	110,429
Level 2 | Obligations of States and Political Subdivisions
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	22,298	24,020
Level 2 | Corporate
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	293,730	278,302
Level 2 | International
Investments, Debt and Equity Securities [Abstract]
Debt securities - available-for-sale, at fair value:	$ 30,444	$ 29,750