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Income Taxes (Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Abstract]
Statutory rate	21.00%	35.00%
State taxes, net of federal tax benefit	2.20%	1.50%
Foreign tax expense and tax rate differential	(0.20%)	(0.80%)
Tax benefit from stock option exercises	(10.80%)	(4.20%)
Other, net	(0.30%)	(0.50%)
Effective income tax rate	11.90%	31.00%

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- Definition

Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Abstract]

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to equity-based compensation costs.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments.

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