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Share-based Compensation - Share and performance-based compensation expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share and performance-based compensation expense [Abstract]
Performance-based share expense	$ 6,300,000	$ 3,000,000.0	$ (100,000)
Service-based share expense	3,300,000	3,500,000	3,800,000
Total share-based compensation expense before income tax	9,600,000	6,500,000	3,700,000
Income tax	0	0	0
Total share-based compensation expense, net of income tax	9,600,000	6,500,000	3,700,000
Share-based payment arrangement, amount capitalized	0	$ 0	$ 0
Unrecognized compensation expense	$ 12,500,000
Weighted average period of expense recognition	2 years

X

- Definition

The amount of expense, gross of income tax, recognized during the period arising from performance-based share arrangements.

+ References

No definition available.

+ Details

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X

- Definition

The amount of expense, gross of income tax, recognized during the period arising from service based compensation arrangements.

+ References

No definition available.

+ Details

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- Definition

Share and performance-based compensation expense [Abstract]

+ References

No definition available.

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

Amount, after tax, of expense for award under share-based payment arrangement.

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No definition available.

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- Definition

Amount of cost capitalized for award under share-based payment arrangement.

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-Name Accounting Standards Codification
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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
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