Employee benefit plans - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Salaries and employee benefits expense	$ 5	$ 83
Common stock available for grant as awards	54,506
Non-Performance-based restricted stock \| 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares or units vesting period	3 years
Performance-based restricted stock units \| 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares or units vesting period	3 years
Cumulative diluted earnings per share period used for conditions for vesting of performance-based restricted stock units	3 years
Average return on equity period used for conditions for vesting of performance-based restricted stock units	3 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Weighted average vesting period	2 years 7 months 6 days
Restricted Stock \| 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Granted shares	16,854
Unrecognized compensation expense	$ 861
Restricted stock units (RSUs) \| 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Granted shares		17,345

The average return on equity period used for conditions for vesting of performance-based restricted stock units.

No definition available.

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- Definition

The cumulative diluted earnings per share period used for conditions for vesting of performance-based restricted stock units.

+ References

No definition available.

+ Details

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- Definition

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

+ 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 (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

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.

+ References

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- Definition

Amount of cost (reversal of cost) for other postretirement benefits. Excludes pension benefits.

+ References

No definition available.

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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

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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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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
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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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

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ 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
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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