Investments (Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 690	$ 691
Due after one year through five years	116,702	47,900
Due after five years through ten years	247,330	332,841
Due after ten years	247,133	276,647
Total debt securities available for sale	611,855	658,079
Estimated Fair Value
Due in one year or less	701	714
Due after one year through five years	118,680	49,385
Due after five years through ten years	254,687	340,852
Due after ten years	251,028	280,535
Estimated Fair Value	$ 625,096	$ 671,486