Computation of Earnings Per Share (Detail) - $ / shares shares in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share Basic And Diluted [Line Items]
Basic earnings per share, Weighted Average Shares	83,462	84,214	83,692	84,155
Potential dilutive effect of restricted stock units outstanding	75	75	49	123
Diluted earnings per share, Weighted Average Shares	83,537	84,289	83,741	84,278
Basic earnings per share, Earnings per Share	$ 0.59	$ (2.58)	$ 1.48	$ (1.25)
Potential dilutive effect of restricted stock units outstanding	(0.01)
Diluted earnings per share, Earnings per Share	$ 0.58	$ (2.58)	$ 1.48	$ (1.25)

Earnings Per Share Basic And Diluted [Line Items]

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- Definition

Incremental common shares attributable to share based payment arrangements, per share.

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- Definition

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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- Definition

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 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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