Share-based payments (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of options granted in the period		$ 1.3
Number of options granted in the period (in shares)		139,000
Average grant price (in usd per share)		$ 9.24
Grant price (in usd per share)		$ 53.24
Time-based shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Performance-based shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Stock options \| First anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	20.00%
Stock options \| Second anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	30.00%
Stock options \| Third anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	50.00%
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate fair value at grant date	$ 10.5	$ 8.3
Granted (in shares)	163,000	155,000
Average grant price (in usd per share)	$ 64.43	$ 53.24

Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Grants In Period, Fair Value

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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).

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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).

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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

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

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- Definition

Gross number of share options (or share units) granted during the period.

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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.

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- Definition

Percentage of vesting of award under share-based payment arrangement.

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- Definition

Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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