Earnings Per Share - Schedule of Calculation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share, Basic And Diluted, By Common Class, Including Two Class Method [Line Items]
Income available to common shareholders	$ 717	$ 19,393
Distributed earnings (distributed capital) to common shareholders - Basic	703	19,019
Distributed and undistributed earnings to common shareholders - Diluted	697	19,029
Weighted average shares outstanding - Basic	29,502,711	29,384,220
Weighted average shares outstanding - Diluted	28,979,168	28,928,276
Earnings per common share - Basic	$ 0.02	$ 0.66
Earnings per common share - Diluted	$ 0.02	$ 0.66
Unvested restricted stock [Member]
Earnings Per Share, Basic And Diluted, By Common Class, Including Two Class Method [Line Items]
Distributed earnings (distributed capital) to unvested restricted stock	(14)	(374)
Undistributed earnings reallocated to unvested restricted stock	$ (6)	$ 10
Earnings per common share - Basic	$ 0.03	$ 0.70
Earnings per common share - Diluted	$ 0.04	$ 0.68

Distributed and undistributed earnings to common shareholders - Basic

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Distributed and undistributed earnings to common shareholders - Diluted

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Distributed and undistributed earnings to unvested restricted stock

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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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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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Earnings allocated (not distributed) to participating securities under the two-class method to the extent that participating securities may share in earnings as if all of the earnings for the period had been distributed.

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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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