Amortized Cost and Estimated Fair Values of investment securities Available-For-Sale by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 2,080	$ 35,544
Due after one year through five years	12,766	3,957
Due after five years through ten years	392,389	382,957
Due after ten years	342,732	368,708
Total debt securities available for sale	749,967	791,166
Estimated Fair Value
Due in one year or less	2,085	36,349
Due after one year through five years	13,285	3,994
Due after five years through ten years	392,339	399,180
Due after ten years	342,852	385,336
Estimated Fair Value	$ 750,561	$ 824,859