Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income allocable to common stockholders	$ 9,048	$ 5,752
Denominator:
Denominator for basic earnings per share - weighted average shares	8,781	8,687
Effect of dilutive employee stock options and warrants	92	73
Denominator for diluted earnings per share - adjusted weighted average shares and assumed exercise	8,873	8,760
Basic:
Net income allocable to common shareholders	$ 1.03	$ 0.66
Diluted:
Net income allocable to common shareholders	$ 1.02	$ 0.66
Outstanding common stock equivalents having no dilutive effect	265	480

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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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 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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