Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income available to common equity	$ 332,911	$ 218,054	$ 591,514	$ 409,230
Less: Income attributable to unvested stock-based compensation awards	(4,354)	(3,338)	(7,881)	(6,272)
Net income available to common shareholders	$ 328,557	$ 214,716	$ 583,633	$ 402,958
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	129,964	127,445	129,708	127,301
Less: Unvested stock-based compensation awards	(1,712)	(1,957)	(1,746)	(1,947)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	765	409	866	402
Adjusted weighted-average shares outstanding	129,017	125,897	128,828	125,756
Diluted earnings per common share	$ 2.55	$ 1.71	$ 4.53	$ 3.20

Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards.

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Income attributable to unvested Stock Based compensation awards diluted.

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Net Income (Loss) Available to Common Stockholders Diluted before Unvested Stock-Based Compensation Awards, Adjustment.

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Unvested stock-based compensation awards.

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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 share based payment arrangements using the treasury stock method.

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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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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