Earnings Per Share - Details of Basic and Diluted Earnings Per Share (EPS) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 30,372	$ 34,119	$ 49,689	$ 50,681
Weighted average common shares outstanding used in basic EPS	43,049	43,251	43,233	43,118
Common shares issuable upon exercise of dilutive stock options and PSAs / RSUs	792	1,077	878	1,095
Weighted average common shares outstanding and common share equivalents used in diluted EPS	43,841	44,328	44,111	44,213
Earnings per share
Basic	$ 0.71	$ 0.79	$ 1.15	$ 1.18
Diluted	$ 0.69	$ 0.77	$ 1.13	$ 1.15

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

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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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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