Earnings Per Common Share - Summary of Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Numerator for both basic and diluted earnings per common share:
Net income	$ 13,887us-gaap_NetIncomeLoss	$ 16,421us-gaap_NetIncomeLoss	$ 16,421us-gaap_NetIncomeLoss
Denominator:
Total average basic common shares outstanding	34,393,137	29,182,183
Effect of dilutive stock options and warrant	85,198	80,497
Total diluted average common shares outstanding	34,478,335	29,262,680
Earnings per common share - basic	$ 0.40us-gaap_EarningsPerShareBasic	$ 0.56us-gaap_EarningsPerShareBasic
Earnings per common share - diluted	$ 0.40us-gaap_EarningsPerShareDiluted	$ 0.56us-gaap_EarningsPerShareDiluted

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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- Definition

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of call options and warrants using the treasury stock method.

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- Definition

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

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