INVESTMENTS - (Gross Unrealized Losses and Related Fair Values for Debt and Equity Securities, Grouped by Duration of Time in Continuous Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value [Abstract]
Less than 12 months	$ 76,371	$ 201,896
12 months or longer	10,091	92,423
Total	86,462	294,319
Gross unrealized losses [Abstract]
Less than 12 months	535	3,539
12 months or longer	57	3,124
Total	592	6,663
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	0	874
12 months or longer	2,287	3,203
Total	2,287	4,077
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months	0	8
12 months or longer	39	157
Total	39	165
Total investments, excluding equity securities, Fair Value, Less than 12 months	76,371	202,770
Total investments, excluding equity securities, Gross Unrealized Losses, Less than 12 months	535	3,547
Total investments, excluding equity securities, Fair Value, 12 months or longer	12,378	95,626
Total investments, excluding equity securities, Gross Unrealized Losses, 12 months or longer	96	3,281
Total investments, excluding equity securities, Fair Value	88,749	298,396
Total investments, excluding equity securities, Gross Unrealized Losses	631	6,828
United States Government Obligations and Authorities [Member]
Fair value [Abstract]
Less than 12 months	49,833	22,673
12 months or longer	2,218	29,727
Total	52,051	52,400
Gross unrealized losses [Abstract]
Less than 12 months	409	246
12 months or longer	17	905
Total	426	1,151
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	0	229
12 months or longer	2,287	3,113
Total	2,287	3,342
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months	0	1
12 months or longer	39	157
Total	39	158
Obligations of States and Political Subdivisions [Member]
Fair value [Abstract]
Less than 12 months	6,810	3,254
12 months or longer	0	4,786
Total	6,810	8,040
Gross unrealized losses [Abstract]
Less than 12 months	22	18
12 months or longer	0	112
Total	22	130
Corporate [Member]
Fair value [Abstract]
Less than 12 months	15,872	160,361
12 months or longer	7,694	53,232
Total	23,566	213,593
Gross unrealized losses [Abstract]
Less than 12 months	94	3,058
12 months or longer	38	1,913
Total	132	4,971
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	0	591
12 months or longer	0	90
Total	0	681
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months	0	6
12 months or longer	0	0
Total	0	6
International [Member]
Fair value [Abstract]
Less than 12 months	3,856	15,608
12 months or longer	179	4,678
Total	4,035	20,286
Gross unrealized losses [Abstract]
Less than 12 months	10	217
12 months or longer	2	194
Total	12	411
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	0	54
12 months or longer	0	0
Total	0	54
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months	0	1
12 months or longer	0	0
Total	$ 0	$ 1