Stock-based compensation - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Directors
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Stock granted	1,195		39,104
Restricted Stock Units (RSUs)
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Stock-Based Compensation, vesting rights	Unless otherwise stated in an agreement, the compensation cost associated with the shares of restricted stock granted prior to 2021 was determined based on a two-prong vesting schedule. The first part is vested ratably over five or four years commencing at the date of grant (“the graduated vesting portion”) and the second part is vested at termination of employment after attainment of 55 years of age and 10 years of service or 60 years of age and 5 years of service (“the retirement vesting portion”). The graduated vesting portion is accelerated at termination of employment after attaining the earlier of 55 years of age and 10 years of service or 60 years of age and 5 years of service. Restricted stock granted on or after 2021 will vest ratably in equal annual installments over a period of 4 years or 3 years, depending on the classification of the employee. The vesting schedule is accelerated at termination of employment after attaining the earlier of 55 years of age and 10 years of service or 60 years of age and 5 years of service.
Restricted Stock Units (RSUs) | Executive Officers
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Stock granted	77,859	69,488
Restricted Stock Expense (Benefit)	$ 6,400	$ 4,400
Incentive award, tax benefit (expense)	600	$ 300
Fair Market Value of stock vested	13,200
Windfall Net Of Shortfall	1,400
Restricted Stock Units (RSUs) | Executive Officers | Share Vesting On Grant Date
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Fair Market Value of stock vested	$ 9,500
Restricted Stock Units (RSUs) | Directors
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Stock granted	1,195	1,029
Restricted Stock Expense (Benefit)	$ 98	$ 67
Incentive award, tax benefit (expense)	18	$ 13
Fair Market Value of stock vested	$ 98
Performance Based Shares | Minimum
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vested and expected to vest range based on shareholder return	50.00%
Performance Based Shares | Maximum
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vested and expected to vest range based on shareholder return	150.00%
Performance Based Shares | Executive Officers
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total unrecognized compensation cost related to non-vested restricted stock awards and performance shares to members of management	$ 11,400
Stock granted	65,225	57,715
Restricted Stock Expense (Benefit)	$ 5,000	$ 3,600
Incentive award, tax benefit (expense)	$ 300	$ 100
Stock-Based Compensation, vesting rights	The number of shares that will ultimately vest ranges from 50% to a 150% of target based on both market (TSR) and performance (ROATCE) conditions. The performance shares vest at the end of the three-year performance cycle. If a participant terminates employment after attaining the earlier of 55 years of age and 10 years of service or 60 years of age and 5 years of service, the performance shares shall continue outstanding and vest at the end of the performance cycle.
Performance Based Shares | Executive Officers | Weighted Average
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total unrecognized compensation cost related to non-vested restricted stock awards and performance shares to members of management, period of recognition (in years)	1 year 9 months 14 days