INVESTMENTS (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale Securities, Debt maturities, Amortized cost:
One year or less	$ 38,343	$ 46,189
Over one through five years	181,014	177,982
Over five through ten years	160,332	150,557
Over ten years	1,216	1,916
Amortized cost	380,905	376,644
Available-for-sale Securities, Debt maturities, Fair value:
One year or less	38,399	46,231
Over one through five years	182,264	177,899
Over five through ten years	162,048	148,783
Over ten years	1,199	1,843
Fair value	383,910	374,756
Held-to-maturity Securities, Debt maturities, Amortized cost [Abstract]
One year or less	135	170
Over one through five years	1,858	1,719
Over five through ten years	3,428	3,662
Amortized cost	5,421	5,551
Held-to-maturity Securities, Debt Maturities, Fair value:
One year or less	135	170
Over one through five years	1,892	1,750
Over five through ten years	3,334	3,553
Fair value	5,361	5,473
Total Investments [Abstract]
Amortized cost	386,326	382,195
Fair value	$ 389,271	$ 380,229