Stock compensation and other employee benefit plans - Assumptions used to value option awards (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Black-Scholes-Merton pricing formula weighted-average assumptions:
Expected life (in years)	7 years 8 months 19 days	6 years 25 days	5 years 11 months 1 day
Risk Free Interest Rate	1.32%	1.60%	1.94%
Volatility	56.47%	51.57%	52.90%
Dividend yield	0.00%	0.00%	0.00%
Valuations:
Grant-date fair value per option (post-split)	$ 4.79	$ 2.86	$ 1.29
Intrinsic value of options exercised (in thousands)	$ 22,852
Average intrinsic value per share of options exercised	$ 8.05

Black-Scholes-Merton pricing formula weighted-average assumptions:

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- Definition

Valuations:

+ References

No definition available.

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- Definition

Fair value per share that would be issued upon settlement of option contract indexed to equity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123477628&loc=d3e90205-114008

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- Definition

Per share or unit weighted-average intrinsic value of award vested under share-based payment arrangement. Excludes share and unit options.

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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.

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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.

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- Definition

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

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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.

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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809

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