Employee Thrift Plan - Additional Information (Detail) (Employee Thrift Plan [Member], USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Bank's expense related to the thrift plan	$ 633,000	$ 545,000	$ 566,000
Thrift Plan owns outstanding shares	313,804
Percentage of outstanding shares owns with thrift plan	3.40%

- Definition

The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

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