Amortized Cost and Estimated Fair Values of Debt Securities Held-To-Maturity by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 2,319	$ 7,431
Due after one year through five years	3,251	4,653
Due after five years through ten years	128,246	116,735
Due after ten years	92,641	86,995
Total debt securities held-to-maturity	226,457	215,814
Estimated Fair Value
Due in one year or less	2,355	7,523
Due after one year through five years	3,269	4,725
Due after five years through ten years	126,598	120,074
Due after ten years	88,616	89,702
Total debt securities held-to-maturity	$ 220,838	$ 222,024