INVESTMENTS (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 54,125	$ 12,789
Due after one year through five years	244,147	180,109
Due after five years through ten years	288,396	228,484
Due after ten years	371,436	306,771
Total debt securities available for sale	958,104	728,153
Estimated Fair Value
Due in one year or less	54,522	12,889
Due after one year through five years	245,061	184,264
Due after five years through ten years	281,183	227,688
Due after ten years	361,498	304,454
Estimated Fair Value	$ 942,264	$ 729,295