Share-based compensation plans - Option Activity (Details)	6 Months Ended
Jun. 30, 2022 $ / shares shares
Performance-Based Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, shares \| shares	946,500
Expired, shares \| shares	(15,300)
Exercised, shares \| shares	(400,000.0)
Ending balance, shares \| shares	531,200
Weighted Average Grant Date Fair Value Per Share
Beginning balance (dollars per share) \| $ / shares	$ 10.25
Expired (dollars per share) \| $ / shares	17.92
Exercised (dollars per share) \| $ / shares	5.92
Ending balance (dollars per share) \| $ / shares	$ 13.29
Time Based Vesting Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, shares \| shares	177,100
Expired, shares \| shares	(15,500)
Ending balance, shares \| shares	161,600
Weighted Average Grant Date Fair Value Per Share
Beginning balance (dollars per share) \| $ / shares	$ 21.42
Expired (dollars per share) \| $ / shares	21.51
Ending balance (dollars per share) \| $ / shares	$ 21.41

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

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

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

+ References

No definition available.

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- Definition

Number of share options (or share units) exercised during the current period.

+ References

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