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, 2016	Dec. 31, 2015
Fair value [Abstract]
Less than 12 months	$ 219,575	$ 154,742
12 months or longer	3,984	4,614
Total fair value	223,559	159,356
Gross unrealized losses [Abstract]
Less than 12 months	4,152	3,804
12 months or longer	70	145
Total gross unrealized losses	4,222	3,949
Debt Securities [Member]
Fair value [Abstract]
Less than 12 months	214,874	142,952
12 months or longer	3,550	4,530
Total fair value	218,424	147,482
Gross unrealized losses [Abstract]
Less than 12 months	3,899	1,954
12 months or longer	35	139
Total gross unrealized losses	3,934	2,093
United States Government Obligations and Authorities [Member]
Fair value [Abstract]
Less than 12 months	45,255	30,464
12 months or longer	111	659
Total fair value	45,366	31,123
Gross unrealized losses [Abstract]
Less than 12 months	850	303
12 months or longer	3	17
Total gross unrealized losses	853	320
Obligations of States and Political Subdivisions [Member]
Fair value [Abstract]
Less than 12 months	103,724	16,652
12 months or longer	1,007
Total fair value	104,731	16,652
Gross unrealized losses [Abstract]
Less than 12 months	2,066	40
12 months or longer	1
Total gross unrealized losses	2,067	40
Corporate [Member]
Fair value [Abstract]
Less than 12 months	59,970	87,176
12 months or longer	2,427	3,590
Total fair value	62,397	90,766
Gross unrealized losses [Abstract]
Less than 12 months	864	1,420
12 months or longer	31	70
Total gross unrealized losses	895	1,490
International [Member]
Fair value [Abstract]
Less than 12 months	5,925	8,660
12 months or longer	5	281
Total fair value	5,930	8,941
Gross unrealized losses [Abstract]
Less than 12 months	119	191
12 months or longer		52
Total gross unrealized losses	119	243
Equity Securities [Member]
Fair value [Abstract]
Less than 12 months	4,701	11,790
12 months or longer	434	84
Total fair value	5,135	11,874
Gross unrealized losses [Abstract]
Less than 12 months	253	1,850
12 months or longer	35	6
Total gross unrealized losses	$ 288	$ 1,856