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Stock-based Compensation - Weighted Average Assumptions of Stock Option (Details) - Stock Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.94%	2.53%	2.65%
Expected term (years)	6 years	6 years	6 years
Volatility	53.18%	48.05%	47.56%
Dividend yield	6.93%	2.81%	1.42%
Fair value per stock option	$ 3.74	$ 13.66	$ 20.47

X

- Definition

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

+ References

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

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)(iii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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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.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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