FAIR VALUE - (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	$ 526,265	$ 428,641
Equity securities, at fair value	20,039	17,758
Total investments, at fair value	546,304	446,399
Fair value transfers	0	0	$ 0
United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	194,193	127,868
Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	24,020	9,767
Corporate [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	278,302	268,731
International [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	29,750	22,275
Level 1 [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	83,764	43,918
Equity securities, at fair value	17,361	16,037
Total investments, at fair value	101,125	59,955
Level 1 [Member] | United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	83,764	43,918
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Level 1 [Member] | Corporate [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Level 1 [Member] | International [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Level 2 [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	442,501	384,723
Equity securities, at fair value	2,678	1,721
Total investments, at fair value	445,179	386,444
Level 2 [Member] | United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	110,429	83,950
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	24,020	9,767
Level 2 [Member] | Corporate [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	278,302	268,731
Level 2 [Member] | International [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	29,750	22,275
Fair Value, Inputs, Level 3
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Equity securities, at fair value	0	0
Total investments, at fair value	0	0
Fair Value, Inputs, Level 3 | United States Government Obligations and Authorities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Fair Value, Inputs, Level 3 | Obligations of States and Political Subdivisions [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Fair Value, Inputs, Level 3 | Corporate [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	0	0
Fair Value, Inputs, Level 3 | International [Member]
Investments, Debt and Equity Securities [Abstract]
Debt securities, at fair value	$ 0	$ 0