Stock-based compensation - Restricted Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Restricted stock disclosures
Stock-based compensation.	$ 2,558	$ 2,319
Unvested restricted common stock units
Shares
Balance, beginning (in shares)	1,112,563
Granted (in shares)	622,050
Vested (in shares)	(374,417)
Forfeited (in shares)	(24,037)
Balance, ending (in shares)	1,336,159
Weighted Average Grant Date Fair Value Per Share
Balance, beginning (in dollars per share)	$ 5.27
Granted (in dollars per share)	7.24
Vested (in dollars per share)	5.44
Forfeited (in dollars per share)	3.80
Balance, ending (in dollars per share)	$ 6.17
Restricted stock disclosures
Vesting period	3 years
Stock-based compensation.	$ 841	$ 792
Unrecognized stock-based compensation expense	$ 7,300
Remaining weighted-average remaining vesting period	2 years 4 months 24 days

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

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

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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.

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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.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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