Capital Stock - Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income available to common shareholders	$ 105,617	$ 74,127	$ 263,141	$ 157,226
Effect of dilutive securities:	0	0	0	0
Dilutive net income available to common shareholders	$ 105,617	$ 74,127	$ 263,141	$ 157,226
Denominator:
Weighted average basic shares (shares)	187,779,406	187,729,765	187,770,626	187,726,618
Effect of dilutive securities (shares)	363,145	195,281	398,467	155,996
Weighted average dilutive shares (shares)	188,142,551	187,925,046	188,169,093	187,882,614
Net income per average share attributable to common stockholders - Basic (usd per share)	$ 0.56	$ 0.39	$ 1.40	$ 0.84
Net income per average share attributable to common stockholders - Diluted (usd per share)	$ 0.56	$ 0.39	$ 1.40	$ 0.84

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise stock options, restrictive stock units (RSUs), convertible preferred stock of an employee stock ownership plan (ESOP), and other dilutive convertible securities.

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