Deposits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deposits [Abstract]
Balance of accounts with more than $100,000 balance	$ 702.4us-gaap_TimeDeposits100000OrMore	$ 611.9us-gaap_TimeDeposits100000OrMore
Interest expenses on accounts with more than $100,000 balance	1.1	1.1	1.5
Balance of certificates of deposit with single public depositor	$ 280.0
Certificate of deposits, Maturity	January through March 2015

- Definition

A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details