INVESTMENTS (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in one year or less	$ 12,789	$ 7,493
Due after one year through five years	180,109	156,953
Due after five years through ten years	228,484	282,468
Due after ten years	306,771	282,708
Total debt securities available for sale	728,153	729,622
Estimated Fair Value
Due in one year or less	12,889	7,541
Due after one year through five years	184,264	162,233
Due after five years through ten years	227,688	282,713
Due after ten years	304,454	279,844
Estimated Fair Value	$ 729,295	$ 732,331