Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 72,163us-gaap_NetIncomeLoss	$ 61,188us-gaap_NetIncomeLoss
Less: Preferred stock dividends	2,016	2,016
Net income available to common shareholders	70,147	59,172
Less: Earnings allocated to participating securities	237	226
Distributed earnings allocated to common stock	32,179us-gaap_DistributedEarnings	30,371us-gaap_DistributedEarnings
Undistributed earnings allocated to common stock	37,731us-gaap_UndistributedEarnings	28,575us-gaap_UndistributedEarnings
Net earnings allocated to common stock	$ 69,910	$ 58,946
Weighted-average shares outstanding for basic earnings per common share	63,094,391	60,701,280
Dilutive effect of stock compensation	685,043	886,260
Weighted-average shares outstanding for diluted earnings per common share	63,779,434	61,587,540

Net Income Loss Available To Common Stock After Participating Securities Allocation

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The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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- Definition

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 aggregate value of preferred stock dividends and other adjustments necessary to derive net income apportioned to common stockholders.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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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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