Equity Based Compensation Option and SAR Assumptions (Details)	12 Months Ended
Dec. 31, 2018 $ / shares
2018 Grants Graded Vesting
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	47.52%
Expected volatility, maximum	49.42%
Risk free rate, minimum	1.56%
Risk free rate, maximum	2.92%
Fair value per share	$ 15.00
2018 Grants Graded Vesting \| Minimum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.00%
Expected term	4 years 4 months 17 days
2018 Grants Graded Vesting \| Maximum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.33%
Expected term	4 years 7 months 13 days
2017 Grants Graded Vesting
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	47.49%
Expected volatility, maximum	49.18%
Risk free rate, minimum	0.60%
Risk free rate, maximum	2.58%
Fair value per share	$ 8.08
2017 Grants Graded Vesting \| Minimum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.41%
Expected term	4 years 4 months 13 days
2017 Grants Graded Vesting \| Maximum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	3.72%
Expected term	4 years 9 months 26 days
2016 Grants Graded Vesting
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	51.31%
Expected volatility, maximum	54.12%
Risk free rate, minimum	0.18%
Risk free rate, maximum	2.47%
Fair value per share	$ 5.67
2016 Grants Graded Vesting \| Minimum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	1.84%
Expected term	4 years 9 months
2016 Grants Graded Vesting \| Maximum
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	3.72%
Expected term	4 years 10 months 13 days

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 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.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

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.

+ References

No definition available.

+ Details

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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

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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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)
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-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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