Calculation for Basic and Diluted Earnings per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Net income	$ 5,958us-gaap_NetIncomeLoss	$ 5,725us-gaap_NetIncomeLoss
Dividends on preferred stock	105	228
Net income available to common shareholders	$ 5,853	$ 5,497
Weighted average number of common shares outstanding, basic	18,633,574	18,423,123
Convertible preferred stock	677,043	1,048,486
Contingently issuable shares	11,411	11,672
Weighted average number of common shares outstanding, diluted	19,344,443	19,506,647
Basic earnings per common share	$ 0.31us-gaap_EarningsPerShareBasic	$ 0.30us-gaap_EarningsPerShareBasic
Diluted earnings per common share	$ 0.31us-gaap_EarningsPerShareDiluted	$ 0.29us-gaap_EarningsPerShareDiluted
Stock Option
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Stock attributable to share based compensation	21,159	22,636
Antidilutive potential common shares	136,382	245,030
Restricted Stock
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Stock attributable to share based compensation	1,256	730

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible preferred stock using the if-converted method.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The amount of preferred stock dividends that is an adjustment to net income apportioned to common stockholders.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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