Employee benefit plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Components of net periodic pension cost:
Salaries and employee benefits expense	$ 7,851	$ 7,250	$ 15,891	$ 13,820
Pension Benefits
Components of net periodic pension cost:
Salaries and employee benefits expense	308	342	597	648
Interest cost	114	105	228	210
Expected return on plan assets	(352)	(322)	(704)	(644)
Amortization of unrecognized net gain	50	76	99	152
Net periodic benefit	$ (188)	$ (141)	$ (377)	$ (282)