INVESTMENTS (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Debt maturities, Amortized cost:
One year or less	$ 46,189	$ 24,470
Over one through five years	177,982	170,797
Over five through ten years	150,557	142,728
Over ten years	1,916	26
Amortized cost	376,644	338,021
Available-for-sale Securities, Debt maturities, Fair value:
One year or less	46,231	24,488
Over one through five years	177,899	171,113
Over five through ten years	148,783	143,545
Over ten years	1,843	32
Amortized cost	374,756	339,178
Held-to-maturity Securities, Debt maturities, Amortized cost [Abstract]
One year or less	170	486
Over one through five years	1,719	1,899
Over five through ten years	3,662	4,234
Amortized cost	5,551	6,619
Held-to-maturity Securities, Debt Maturities, Fair value:
One year or less	170	487
Over one through five years	1,750	1,915
Over five through ten years	3,553	4,037
Estimated fair value	5,473	6,439
Total Investments [Abstract]
Amortized cost	382,195	344,640
Estimated fair value	$ 380,229	$ 345,617