Summary of Carrying Amount and Estimated Fair Value of Held-to-Maturity Debt Securities and Amortized Cost and Estimated Fair Value of Available-for-Sale Debt Securities by Contractual Maturity (Parenthetical) (Detail) (Other Debt Securities, USD $)	Dec. 31, 2011
Available-for-Sale Securities, Carrying Amount:
Due after ten years	$ 36,754,000	[1]
Held-to-Maturity Securities, Carrying Amount:
Due after ten years	162,367,000	[1]
Pooled Debt Securities Funds
Available-for-Sale Securities, Carrying Amount:
Due after ten years	15,500,000
Held-to-Maturity Securities, Carrying Amount:
Due after ten years	$ 629,000

[1] Includes corporate bonds and capital trust notes. Included in capital trust notes are $15.5 million and $629,000 of pooled trust preferred securities available for sale and held to maturity, respectively, all of which are due after ten years. The remaining capital trust notes consist of single-issue trust preferred securities.