INVESTMENTS (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 40,224	$ 12,789
Due after one year through five years	265,558	180,109
Due after five years through ten years	278,570	228,484
Due after ten years	403,913	306,771
Total debt securities available for sale	988,265	728,153
Estimated Fair Value
Due in one year or less	40,564	12,889
Due after one year through five years	267,383	184,264
Due after five years through ten years	273,027	227,688
Due after ten years	395,682	304,454
Estimated Fair Value	$ 976,656	$ 729,295