Employee benefit plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Components of net periodic pension cost:
Salaries and employee benefits expense	$ 8,474	$ 7,829	$ 24,365	$ 21,649
Pension Benefits
Components of net periodic pension cost:
Salaries and employee benefits expense	373	343	970	991
Interest cost	114	105	342	315
Expected return on plan assets	(352)	(322)	(1,056)	(966)
Amortization of unrecognized net gain	50	76	149	227
Net periodic benefit	$ (188)	$ (141)	$ (565)	$ (424)