Calculation for Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Net income	$ 6,255	$ 6,175	$ 12,339	$ 12,133
Dividends on preferred stock				105
Net income available to common shareholders	$ 6,255	$ 6,175	$ 12,339	$ 12,028
Weighted average common shares outstanding, basic	17,414,320	18,831,907	17,636,783	18,733,288
Convertible preferred stock				336,651
Total dilutive effect of potential common shares	48,525	28,377	38,345	362,120
Weighted average common shares outstanding, diluted	17,462,845	18,860,284	17,675,128	19,095,408
Basic earnings per common share	$ 0.36	$ 0.33	$ 0.70	$ 0.64
Diluted earnings per common share	$ 0.36	$ 0.33	$ 0.70	$ 0.64
Total potential antidilutive shares	130,165	136,382	147,713	136,382
Stock Options
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Stock attributable to share based compensation	32,365	24,389	29,605	22,914
Total potential antidilutive shares	130,165	136,382	147,713	136,382
Restricted Stock
Calculation For Basic And Diluted Earnings Per Common Share [Line Items]
Stock attributable to share based compensation	16,160	3,988	8,740	2,555

Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]

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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 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 sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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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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