INVESTMENTS (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 58,653	$ 12,789
Due after one year through five years	263,959	180,109
Due after five years through ten years	278,132	228,484
Due after ten years	346,732	306,771
Total debt securities available for sale	947,476	728,153
Estimated Fair Value
Due in one year or less	59,057	12,889
Due after one year through five years	263,262	184,264
Due after five years through ten years	269,055	227,688
Due after ten years	334,781	304,454
Estimated Fair Value	$ 926,155	$ 729,295