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Income Taxes (Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Statutory rate									21.00%	21.00%	21.00%
State taxes, net of federal tax benefit									3.00%	2.40%	1.90%
Foreign tax expense and tax rate differential									(0.40%)	0.00%	(0.10%)
Tax benefit from stock option exercises									(1.10%)	(1.90%)	(3.80%)
Research and development tax credit									(1.00%)	(1.10%)	(0.80%)
Foreign-Derived Intangible Income Deduction (FDII)									(0.30%)	(0.20%)	(0.20%)
Other, net									0.10%	0.40%	(0.40%)
Effective income tax rate	19.60%	21.40%	23.30%	21.50%	19.50%	18.90%	22.10%	22.10%	21.30%	20.60%	17.60%

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- Definition

Effective Income Tax Rate Reconciliation, Tax Benefit From Stock Option Exercises, Percent

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Effective Income Tax Rate Reconciliation,Tax Cuts And Jobs Act Of 2017, Foreign Derived Intangible Income Deduction, Percent

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
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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.

+ References

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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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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 research tax credit.

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