Amortized Cost and Estimated Fair Values of Debt Securities Held-To-Maturity by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 2,765	$ 7,431
Due after one year through five years	3,253	4,653
Due after five years through ten years	132,577	116,735
Due after ten years	87,399	86,995
Total debt securities held-to-maturity	225,994	215,814
Estimated Fair Value
Due in one year or less	2,787	7,523
Due after one year through five years	3,264	4,725
Due after five years through ten years	130,588	120,074
Due after ten years	83,415	89,702
Total debt securities held-to-maturity	$ 220,054	$ 222,024