Total Income Tax expense Applying U.S.Federal Income Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components Of Income Tax Expense Benefit [Line Items]
Computed tax expense at statutory federal rates	$ 19,911	$ 12,328	$ 5,660
Increase (decrease) in taxes resulting from:
State taxes, net of federal income tax benefit	1,947	1,374	742
Domestic production deduction	(1,661)	(826)	(345)
Income tax credits	(395)	(343)	(315)
Other expenses	224	622	(552)
Total income tax expense (benefit)	$ 20,026	$ 13,155	$ 5,190

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- Definition

The sum of domestic current and deferred income tax expense or benefit attributable to continuing operations.

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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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