Stock Incentive Plans - Stock Options, Valuation Assumptions (Details) - Stock Option - $ / shares	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.35%	2.68%
Risk-free interest rate, maximum	2.64%	2.90%
Volatility, minimum	28.02%	27.91%
Volatility, maximum	28.59%	30.65%
Dividend yield	0.00%	0.00%
Weighted average fair value per stock option (in usd per share)	$ 8.74	$ 11.02
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average life of options	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average life of options	6 years 6 months	6 years 6 months

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

No definition available.

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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.

+ References

+ Details

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- Definition

The estimated measure of the maximum 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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No definition available.

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The estimated measure of the minimum 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.

+ References

No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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
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