Calculation for Basic and Diluted Earnings per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Net income	$ 7,141	$ 6,001
Dividends on preferred stock	258	283
Net income available to common shareholders	$ 6,883	$ 5,718
Weighted average common shares outstanding, basic	20,032,694	17,849,376
Diluted shares for stock options	159,323	34,998
Weighted average convertible preferred shares	1,202,049	1,305,549
Weighted average common shares outstanding, diluted	21,394,066	19,189,923
Basic earnings per common share	$ 0.34	$ 0.32
Diluted earnings per common share	$ 0.33	$ 0.31

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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 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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