Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 31,234	$ 30,000	$ 25,180	$ 110,868
Income tax expense using estimated annual effective income tax rate	12,024	11,920	9,694	44,051
Out-of-period adjustment related to non-deductible expenses in 2011	0	0	757	0
Impact of discrete item, net	(148)	0	(808)	464
Changes in effective tax rates	1,426	1,401	1,400	0
Reduction of valuation allowance	0	(870)	0	(870)
Income tax expense	$ 13,302	$ 12,451	$ 11,043	$ 43,645

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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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to changes in the valuation allowance for deferred tax assets in the period.

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- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to changes in the income tax rates under enacted tax laws in the period.

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- Definition

The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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