Investments (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 992	$ 691
Due after one year through five years	127,163	47,900
Due after five years through ten years	229,704	332,841
Due after ten years	232,068	276,647
Total debt securities available for sale	589,927	658,079
Estimated Fair Value
Due in one year or less	1,004	714
Due after one year through five years	130,361	49,385
Due after five years through ten years	238,574	340,852
Due after ten years	236,957	280,535
Estimated Fair Value	$ 606,896	$ 671,486