Stock-Based Compensation, Assumptions Used to Estimate Fair Value of Options Granted (Details)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Assumptions [Abstract]
Risk-free interest rate	2.00%
Expected dividend rate	0.00%
Minimum [Member]
Assumptions [Abstract]
Expected life of options	1 year
Assumed volatility	26.80%
Maximum [Member]
Assumptions [Abstract]
Expected life of options	1 year 3 months 18 days
Assumed volatility	27.30%
Stock Options [Member]
Assumptions [Abstract]
Expected dividend rate	0.00%	0.00%
Stock Options [Member] \| Minimum [Member]
Assumptions [Abstract]
Expected life of options	7 years	5 years
Risk-free interest rate	2.90%	1.90%
Assumed volatility	34.40%	41.20%
Stock Options [Member] \| Maximum [Member]
Assumptions [Abstract]
Expected life of options	7 years 6 months	6 years 3 months 18 days
Risk-free interest rate	3.00%	2.10%
Assumed volatility	35.40%	45.80%

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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