Earnings per Share - Schedule of Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net Income	$ 19,725us-gaap_NetIncomeLoss	$ 21,767us-gaap_NetIncomeLoss
Noncontrolling interests	(383)	171
Net Income Attributable to Common Stockholders	$ 19,342	$ 21,938
Shares:
Basic: Weighted-average number of shares outstanding	8,964	9,116
Plus: Incremental shares from assumed conversion of dilutive instruments	187	245
Diluted: Weighted-average number of shares outstanding	9,151	9,361
Earnings per share - basic	$ 2.16us-gaap_EarningsPerShareBasic	$ 2.41us-gaap_EarningsPerShareBasic
Earnings per share - diluted	$ 2.11us-gaap_EarningsPerShareDiluted	$ 2.34us-gaap_EarningsPerShareDiluted

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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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Amount of income (loss) from continuing operations attributable to the noncontrolling interest. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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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.

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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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