Share-based compensation - Stock appreciation rights - Awards, simulation inputs, outputs (Details) - $ / shares	Mar. 04, 2021	Mar. 04, 2020	Mar. 07, 2019	Apr. 04, 2018	Jan. 15, 2016	Mar. 06, 2015	Sep. 01, 2014	Mar. 12, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Valuation Method	Black-Scholes	Black-Scholes	Black-Scholes	Black-Scholes	Monte Carlo	Monte Carlo	Monte Carlo	Monte Carlo
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SARs Awarded (in shares)	610,691	549,020	560,000	1,719,733	205,519	37,797	5,595	22,118
Exercise Price (in dollars per share)	$ 4.28	$ 5.25	$ 5.10	$ 7.40	$ 9.20	$ 10.25	$ 13.91	$ 13.66
Vesting Period (in years)	3 years	3 years	3 years	3 years	3 years	3 years	3 years	3 years
Grant Price (in dollars per share)	$ 4.28	$ 5.25	$ 5.10	$ 7.40	$ 9.20	$ 10.25	$ 13.91	$ 13.66
Dividend Yield (in hundredths)	0.00%	0.00%	0.00%	0.00%	6.63%	3.90%	2.88%	2.93%
Risk-free rate of Return (in hundredths)	0.66%	0.73%	2.43%	2.51%	1.79%	1.90%	2.20%	2.06%
Expected Volatility (in hundredths)	55.39%	46.42%	43.65%	40.59%	58.09%	61.38%	53.60%	56.31%
Weighted Average Fair Value at grant date (in dollars per share)	$ 1.93	$ 2.04	$ 2.00	$ 2.67	$ 2.20	$ 2.98	$ 4.20	$ 4.17
Average Expected Exercise Life	4 years 6 months	4 years 6 months	4 years 6 months	4 years 3 months
Stock appreciation rights \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average Expected Exercise Life					5 years	5 years	5 years	5 years
Stock appreciation rights \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average Expected Exercise Life					4 years	4 years 2 months 12 days	4 years 6 months	4 years 7 months 6 days

This line item represents the average expected exercise life of units grant during the period.

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- Definition

Granted price per share of equity-based compensation awards granted. Excludes stock and unit options.

+ References

No definition available.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 2
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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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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

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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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- Definition

Description of method used to estimate fair value of award under share-based payment arrangement.

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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
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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

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

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