Earnings Per Share - Reconciles Numerator and Denominator of Basic and Diluted Earnings Per Share Computations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator for EPS:
Net income	$ 22,330us-gaap_NetIncomeLoss	$ 13,549us-gaap_NetIncomeLoss
Less: Preferred stock dividends	(2)	(5)
Income available to common stockholders	$ 22,328	$ 13,544
Denominator for EPS:
Weighted average common shares outstanding	34,578	33,422
Plus: Assumed conversion of stock-based compensation	1,468	2,140
Assumed conversion of preferred stock	35	79
Weighted average diluted common shares outstanding	36,081	35,641
Basic earnings per common share	$ 0.65us-gaap_EarningsPerShareBasic	$ 0.41us-gaap_EarningsPerShareBasic
Diluted earnings per common share	$ 0.62us-gaap_EarningsPerShareDiluted	$ 0.38us-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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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 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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