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Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Mar. 31, 2013	Mar. 31, 2012
Income Tax Disclosure [Line Items]
Provision for income taxes	$ 24,134,000	$ 21,853,000
Effective tax rate	28.20%	29.50%
Reasonably possible change in unrecognized tax benefits over next 12 months, lower range	0
Reasonably possible change in unrecognized tax benefits over next 12 months, upper range	$ 2,700,000

- Definition

A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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- Definition

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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