Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Number of shares issued pursuant to the terms of a deferred compensation arrangement.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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Noninterest expense related to directors' fees which are fees paid by an Entity to its directors. Directors' fees may be paid in addition to salary and other benefits.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from exercise of stock options			$ 0.3
Tax benefit from exercise of stock options			0.2
Share-based compensation expense	$ 1.2	$ 1.1	$ 2.4	$ 2.0
Common Stock \| Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation shares issued			16,312
Noninterest Expense Directors Fees			$ 0.4
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted			158,581
Vesting period	3 years
Restricted Stock Units \| Bonus Recognition and Retention Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	84,392
Vesting period	5 years