Earnings Per Share - Computation of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 144,050us-gaap_NetIncomeLoss	$ 117,804us-gaap_NetIncomeLoss	$ 110,410us-gaap_NetIncomeLoss
Less: Preferred stock dividends	8,352us-gaap_DividendsPreferredStockCash
Net income available to common stockholders	$ 135,698	$ 117,804	$ 110,410
Basic weighted average common shares outstanding	167,347,906	146,186,982	139,135,272
Net effect of dilutive stock options, warrants, restricted stock and convertible debt	1,730,939	1,622,522	1,504,893
Diluted weighted average common shares outstanding	169,078,845	147,809,504	140,640,165
Basic earnings per common share	$ 0.81us-gaap_EarningsPerShareBasic	$ 0.81us-gaap_EarningsPerShareBasic	$ 0.79us-gaap_EarningsPerShareBasic
Diluted earnings per common share	$ 0.80us-gaap_EarningsPerShareDiluted	$ 0.80us-gaap_EarningsPerShareDiluted	$ 0.79us-gaap_EarningsPerShareDiluted

Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.

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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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